From a690c8e7a2e92be336a8cb243f27f1f91f799416 Mon Sep 17 00:00:00 2001 From: Fernando Cacciola Date: Fri, 2 Nov 2007 22:55:49 +0000 Subject: [PATCH 01/18] Merged changests from RC_1_34_0 - base rev 33417 [SVN r40704] --- doc/optional.html | 451 ++++++++++++++++++++----------- test/Jamfile.v2 | 2 - test/optional_test.cpp | 58 +++- test/optional_test_ref.cpp | 18 ++ test/optional_test_ref_fail2.cpp | 23 -- 5 files changed, 361 insertions(+), 191 deletions(-) delete mode 100644 test/optional_test_ref_fail2.cpp diff --git a/doc/optional.html b/doc/optional.html index fedf8d9..e216db5 100644 --- a/doc/optional.html +++ b/doc/optional.html @@ -3,6 +3,7 @@ + @@ -23,6 +24,7 @@ HREF="../../../boost/optional/optional.hpp">boost/optional/optional.hpp>
Examples
Optional references
Rebinding semantics for assignment of optional references
+
none_t and none
In-Place Factories
A note about optional<bool>
Exception Safety Guarantees
@@ -138,7 +140,7 @@ necessary in order to do so.

purpose of optional<T> suggests an alternative model: a container that either has a value of T or nothing.

-

As of this writing I don't know of any precedence for a variable-size fixed-capacity (of 1) +

As of this writing I don't know of any precedent for a variable-size fixed-capacity (of 1) stack-based container model for optional values, yet I believe this is the consequence of the lack of practical implementations of such a container rather than an inherent shortcoming of the container model.

@@ -348,7 +350,7 @@ class optional T const& get() const ; T& get() ; - T const& get_value_or( T const& default ) const ; [new in 1.34] + T const& get_value_or( T const& default ) const ; [new in 1.34] T const* operator ->() const ; T* operator ->() ; @@ -383,11 +385,59 @@ template<class T> inline bool operator <= ( optional<T> const& x, op template<class T> inline bool operator >= ( optional<T> const& x, optional<T> const& y ) ; +template<class T> inline bool operator == ( optional<T> const& x, T const& n ) ; [new in 1.34] + +template<class T> inline bool operator != ( optional<T> const& x, T const& n ) ; [new in 1.34] + +template<class T> inline bool operator < ( optional<T> const& x, T const& n ) ; [new in 1.34] + +template<class T> inline bool operator > ( optional<T> const& x, T const& n ) ; [new in 1.34] + +template<class T> inline bool operator <= ( optional<T> const& x, T const& n ) ; [new in 1.34] + +template<class T> inline bool operator >= ( optional<T> const& x, T const& n ) ; [new in 1.34] + +template<class T> inline bool operator == ( T const& n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator != ( T const& n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator < ( T const& n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator > ( T const& n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator <= ( T const& n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator >= ( T const& n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator == ( optional<T> const& x, none_t n ) ; [new in 1.34] + +template<class T> inline bool operator != ( optional<T> const& x, none_t n ) ; [new in 1.34] + +template<class T> inline bool operator < ( optional<T> const& x, none_t n ) ; [new in 1.34] + +template<class T> inline bool operator > ( optional<T> const& x, none_t n ) ; [new in 1.34] + +template<class T> inline bool operator <= ( optional<T> const& x, none_t n ) ; [new in 1.34] + +template<class T> inline bool operator >= ( optional<T> const& x, none_t n ) ; [new in 1.34] + +template<class T> inline bool operator == ( none_t n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator != ( none_t n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator < ( none_t n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator > ( none_t n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator <= ( none_t n, optional<T> const& y ) ; [new in 1.34] + +template<class T> inline bool operator >= ( none_t n, optional<T> const& y ) ; [new in 1.34] + template<class T> inline optional<T> make_optional ( T const& v ) ; [new in 1.34] template<class T> inline optional<T> make_optional ( bool condition, T const& v ) ; [new in 1.34] -template<class T> inline T const& get_optional_value_or ( optional<T> const& opt, T const& default ) ; [new in 1.34] +template<class T> inline T const& get_optional_value_or ( optional<T> const& opt, T const& default ) ; [new in 1.34] template<class T> inline T const& get ( optional<T> const& opt ) ; @@ -457,9 +507,11 @@ used as the parameter.

Example:

- 
#include <boost/none.hpp>
- 
optional<T> n(none) ;
-assert ( !n ) ;
+
+#include <boost/none.hpp>
+optional<int> n(boost::none) ;
+assert ( !n ) ;
+
@@ -476,9 +528,11 @@ in that case, this constructor has no effect.

Example:

-
T v;
+
+T v;
 optional<T> opt(v);
-assert ( *opt == v ) ;

+assert ( *opt == v ) ;
+
@@ -492,29 +546,32 @@ instance of an internal type wrapping the reference 'ref'.

Throws: Nothing.

Example:

-
T v;
+
+T v;
 T& vref = v ;
 optional<T&> opt(vref);
 assert ( *opt == v ) ;
 ++ v ; // mutate referee
-assert (*opt == v); 

+assert (*opt == v); 
+
optional<T (not a ref)>::optional( bool condition, T const& v ) ;
-optional<T&>           ::optional( bool condition, T&       v ) ;
+optional<T&>           ::optional( bool condition, T&       v ) ;

If condition is true, same as:

optional<T (not a ref)>::optional( T const& v )
-optional<T&>           ::optional( T&       v )
+optional<T&>           ::optional( T&       v )

otherwise, same as:

-
optional<T (not a ref)>::optional()
-optional<T&>           ::optional()
+
+optional<T (not a ref)>::optional()
+optional<T&>           ::optional()
@@ -533,7 +590,8 @@ in that case, this constructor has no effect.

Example:

- 
optional<T> uninit ;
+
+optional<T> uninit ;
 assert (!uninit);
 
 optional<T> uinit2 ( uninit ) ;
@@ -562,7 +620,8 @@ is uninitialized.

 reefer to the same object (they alias).

 
Example:

 

-        
optional<T&> uninit ;
+
+optional<T&> uninit ;
 assert (!uninit);
 
 optional<T&> uinit2 ( uninit ) ;
@@ -605,7 +664,8 @@ in that case, this constructor has no effect.
 
Example:

 

 
-
optional<double> x(123.4);
+
+optional<double> x(123.4);
 assert ( *x == 123.4 ) ;
 
 optional<int> y(x) ;
@@ -633,7 +693,8 @@ in that case, this constructor has no effect.
 
Example:

 

 
-
class C { C ( char, double, std::string ) ; } ;
+
+class C { C ( char, double, std::string ) ; } ;
 
 C v('A',123.4,"hello");
 
@@ -649,6 +710,27 @@ assert ( *y == v ) ;
 
 

 
+
optional& optional<T>::operator= ( none_t n ) ;

+

+
Effect: Same as opeator=(optional const& rhs), when rhs is default-constructed (uninitialized).

+
Postconditions: *this is uninitialized

+
Example:

+

+
+#include <boost/none.hpp>
+
+optional<int> def ;
+optional<int> opt(123) ;
+
+opt = boost::none ;
+
+assert ( opt == def ) ;
+

+

+

+
+

+
 
optional& optional<T (not a ref)>::operator= ( T const& rhs ) ;

 

 
Effect: Assigns the value 'rhs' to an optional.

@@ -664,7 +746,8 @@ uninitialized and T's copy constructor fails, *this is left
 properly uninitialized]

 
Example:

 

-    
T x;
+
+T x;
 optional<T> def ;
 optional<T> opt(x) ;
 
@@ -687,7 +770,8 @@ and it references the same object referenced by rhs.

 new object. See here for details on this behavior.

 
Example:

 

-    
int a = 1 ;
+
+int a = 1 ;
 int b = 2 ;
 T& ra = a ;
 T& rb = b ;
@@ -817,7 +901,7 @@ assert ( *opt1 == static_cast<U>(v) ) ;
 

 
void optional<T>::reset() ;

 

-
Deprecated: Same as operator=( detail::none_t );

+
Deprecated: Same as operator=( none_t n);

 

 
 

@@ -852,32 +936,6 @@ assert ( *opt == w ) ;
 
 

 
-
T const& optional<T (not a ref)>::get_value_or( T const& default) const ;
-T&       optional<T (not a ref)>::get_value_or( T&       default ) ;
-
-inline T const& get_optional_value_or ( optional<T (not a ref)> const& o, T const& default ) ;
-inline T&       get_optional_value_or ( optional<T (not a ref)>&       o, T&       default ) ;
-

-

-
Returns: A reference to the contained value, if any, or default

-
Throws: Nothing.

-
Example:

-

-    
T v, z ;
-optional<T> def;
-T const& y = def.get_value_or(z);
-assert ( y == z ) ;
-
-optional<T> opt ( v );
-T const& u = get_optional_value_or(opt,z);
-assert ( u == v ) ;
-assert ( u != z ) ;
-

-  

-    

-

-

-
 
 
T const& optional<T&>::operator*() const ;
 T      & optional<T&>::operator*();

@@ -907,29 +965,66 @@ assert ( *opt == v ) ;

 
 

 
-
T const* optional<T (not a ref)>::get_ptr() const ;
-T*       optional<T (not a ref)>::get_ptr() ;
+
T const& optional<T>::get_value_or( T const& default) const ;
+T&       optional<T>::get_value_or( T&       default ) ;
 
-inline T const* get_pointer ( optional<T (not a ref)> const& ) ;
-inline T*       get_pointer ( optional<T (not a ref)> &) ;
+inline T const& get_optional_value_or ( optional<T> const& o, T const& default ) ;
+inline T&       get_optional_value_or ( optional<T>&       o, T&       default ) ;
+

+

+
Returns: A reference to the contained value (which can be itself a reference), if any, or default

+
Throws: Nothing.

+
Example:

+

+    
T v, z ;
+optional<T> def;
+T const& y = def.get_value_or(z);
+assert ( y == z ) ;
+
+optional<T> opt ( v );
+T const& u = get_optional_value_or(opt,z);
+assert ( u == v ) ;
+assert ( u != z ) ;
+

+  

+    

+

+
+

+
+
T const* optional<T>::get_ptr() const ;
+T*       optional<T>::get_ptr() ;
+
+inline T const* get_pointer ( optional<T> const& ) ;
+inline T*       get_pointer ( optional<T> &) ;
 

 

 
Returns: If *this is initialized, a pointer to the contained
 value; else 0 (null).
 

 
Throws: Nothing.

+
Notes: If T is a reference type, the pointer is to the referenced object

 
Notes: The contained value is permanently stored within *this, so
-you should not hold nor delete this pointer
+you should not hold nor delete this pointer.
 

 
Example:

 

-    
T v;
-optional<T> opt(v);
-optional<T> const copt(v);
-T* p = opt.get_ptr() ;
-T const* cp = copt.get_ptr();
+    
int v=123;
+optional<int> opt(v);
+optional<int> const copt(v);
+int* p = opt.get_ptr() ;
+int const* cp = copt.get_ptr();
 assert ( p == get_pointer(opt) );
 assert ( cp == get_pointer(copt) ) ;
+
+int& rv = v ;
+optional<int&> optr(rv);
+
+*(optr.get_ptr()) = 456 ;
+
+assert ( v == 456 );
+
+
 

 

 

@@ -938,13 +1033,14 @@ assert ( cp == get_pointer(copt) ) ;
 

 
 
-
T const* optional<T (not a ref)>::operator ->() const ;
-T*       optional<T (not a ref)>::operator ->()       ;
+
T const* optional<T>::operator ->() const ;
+T*       optional<T>::operator ->()       ;
 

 

 
Requirements: *this is initialized.

 
Returns: A pointer to the contained value.

 
Throws: Nothing.

+
Notes: If T is a reference type, the pointer is to the referenced object

 
Notes: The requirement is asserted via BOOST_ASSERT().

 
Example:

 

@@ -952,6 +1048,14 @@ T*       optional<T (not a ref)>::operator ->()       ;
 X x ;
 optional<X> opt (x);
 opt->mdata = 2 ;
+
+X& rx = x ;
+
+optional<X&> optr (rx);
+optr->mdata = 4 ;
+
+assert ( x.mdata = 4 ) 
+
 

 

 

@@ -1154,13 +1258,50 @@ assert ( optX != optZ ) ;
   
Throws: Nothing.

 

 
+

+
+bool operator == ( optional<T> const& x, T const& n );
+bool operator != ( optional<T> const& x, T const& n );
+bool operator <  ( optional<T> const& x, T const& n );
+bool operator >  ( optional<T> const& x, T const& n );
+bool operator <= ( optional<T> const& x, T const& n );
+bool operator >= ( optional<T> const& x, T const& n );
+bool operator == ( T const& n, optional<T> const& y );
+bool operator != ( T const& n, optional<T> const& y );
+bool operator <  ( T const& n, optional<T> const& y );
+bool operator >  ( T const& n, optional<T> const& y );
+bool operator <= ( T const& n, optional<T> const& y );
+bool operator >= ( T const& n, optional<T> const& y );
+

+

+  
Returns: The result obtained by replacing the argument 'n' by optional<T>(n).

+

+
+

+
+bool operator == ( optional<T> const& x, none_t n );
+bool operator != ( optional<T> const& x, none_t n );
+bool operator <  ( optional<T> const& x, none_t n );
+bool operator >  ( optional<T> const& x, none_t n );
+bool operator <= ( optional<T> const& x, none_t n );
+bool operator >= ( optional<T> const& x, none_t n );
+bool operator == ( none_t n, optional<T> const& y );
+bool operator != ( none_t n, optional<T> const& y );
+bool operator <  ( none_t n, optional<T> const& y );
+bool operator >  ( none_t n, optional<T> const& y );
+bool operator <= ( none_t n, optional<T> const& y );
+bool operator >= ( none_t n, optional<T> const& y );
+

+

+  
Returns: The result obtained by replacing the argument 'n' by optional<T>().

+

 

 
 
void swap ( optional<T>& x, optional<T>& y );

 
 

 
Effect: If both x and y are initialized, calls swap(*x,*y) using std::swap.

-If only one is initialized, say x, calls: y.reset(*x); x.reset();

+If only one is initialized, say x, calls: y = *x; x = boost:none;

 If none is initialized, does nothing. 

 
Postconditions: The states of x and y interchanged.

 
Throws: If both are initialized, whatever swap(T&,T&) throws.
@@ -1169,7 +1310,7 @@ If only one is initialized, whatever T::T ( T const& ) throws. 

 If only one is initialized, T::~T() and T::T( T const& ) is called. 

 
Exception Safety: If both are initialized, this operation has the exception
 safety guarantees of swap(T&,T&).

-If only one is initialized, it has the same basic guarantee as optional<T>::reset( T const& ). 

+If only one is initialized, it has the same basic guarantee as optional<T>::operator=( T const& ). 

 
Example:

 

       
T x(12);
@@ -1219,12 +1360,12 @@ void receive_async_message()
 
optional<string> name ;
 if ( database.open() )
 {
-  name.reset ( database.lookup(employer_name) ) ;
+  name = database.lookup(employer_name) ;
 }
 else
 {
   if ( can_ask_user )
-    name.reset ( user.ask(employer_name) ) ;
+    name = user.ask(employer_name) ;
 }
 
 if ( name )
@@ -1245,7 +1386,7 @@ else print("employer's name not found!");
     void clip_in_rect ( rect const& rect )
       {
          ....
-         m_clipping_rect.reset ( rect ) ; // initialized here.
+         m_clipping_rect = rect ; // initialized here.
       }
 
     void draw ( canvas& cvs )
@@ -1289,16 +1430,17 @@ some operations are not available in this case:

   
  • Converting assignment
    • 
   
  • InPlace construction
    • 
   
  • InPlace assignment
    • 
-  
  • Value-access via pointer
    • 
 
 
    Also, even though optional<T&> treats it wrapped pseudo-object much as a real
-value, a true real reference is stored so aliasing will ocurr: 
    
+value, a true real reference is stored, thus aliasing can ocurr: 
    
 
 
      
-  
    • Copies of optional<T&> will copy the references but all these references
+  
    • Copies of optional<T&> copies the reference, but all copied references
   will nonetheless reefer to the same object.
      • 
-  
    • Value-access will actually provide access to the referenced object rather
+  
    • Value-access provides access to the referenced object rather
   than the reference itself.
      • 
+  
    • Pointer-access provides a pointer to the referenced object rather
+  than a pointer to the reference itself.
      • 
 
    
 
 
    
@@ -1309,7 +1451,7 @@ Clearly, there is no other choice.
    
 
    int x = 1 ;
 int& rx = x ;
 optional<int&> ora ;
-optional<int&> orb(x) ;
+optional<int&> orb(rx) ;
 ora = orb ; // now 'ora' is bound to 'x' through 'rx'
 *ora = 2 ; // Changes value of 'x' through 'ora'
 assert(x==2); 
@@ -1320,7 +1462,7 @@ referenced object; it's value changes but the reference is never rebound.
    
 int& ra = a ;
 int b = 2 ;
 int& rb = b ;
-ra = rb ; // Changes the value of 'a' to 'b'
+ra = rb ; // Changes the VALUE of 'a' to that of 'b'
 assert(a==b);
 b = 3 ;
 assert(ra!=b); // 'ra' is not rebound to 'b'
@@ -1346,38 +1488,68 @@ C++ references.
    
 It is true that optional<U> strives to behave as much as possible as U does 
 whenever it is initialized; but in the case when U is T&, doing so would result 
 in inconsistent behavior w.r.t to the lvalue initialization state.
    
-
    Imagine optional<T&> forwarding assignment to the referenced object (thus 
-changing the referenced object value but not rebinding), and consider the 
-following code :
    
-
      optional<int&> a = get();
-  int x = 1 ;
-  int& rx = x ;
-  optional<int&> b(rx);
-  a = b ;
+
    Consider the following code :
    
+
    +int x = 1 ;
+int& rx = x ;
+void foo ( optional<int&> & outer )
+{
+  optional<int&> b(rx);
+  outer = b ;
+}
+
    
+
    What should the assignment to 'outer' do?
    
+If 'outer' is uninitialized, the answer is clear: it should bind to 'x' (so we now have 
+a second reference to 'x').
    
+But what if 'outer' is already initialized?
    
+The assignment could change the value of the 
+referenced object (whatever that is), but doing that would be inconsistent with the uninitialized case
+and then you wouldn't be able to reason at compile time about all the references to x since
+the appearance of a new reference to it would depend on wheter the lvalue ('outer')
+is initialized or not.
    
+
    Arguably, if rebinding the reference to another object is wrong for your code, then is 
+likely that binding it for the fist time via assignment instead of intialization is also wrong.
+In that case, you can always just assign the value to the referenced object directly via
+the access operator *opt=value.
    
+
    If rebinding is wrong but first-time binding 
+isn't (via assignment), you can always work around the rebinding semantics using a discriminator:
    
+
    +if ( !opt )
+      opt = value ; // first-time binding
+else *opt = value ; // assign to referee without rebinding 
+
    
+
+
    
+
+
    none_t and none
    
+
    optional<T> supports uninitialized states with a convenient syntax via a constant of 
+the implementation-defined type boost::none_t, identified as boost::none.
    
+
    Starting with Boost version 1.34.0, both boost::none_t and boost::none are
+included in boost/none.hpp, which is automatically included by boost/optional/optional.hpp
+
    
+
    This contant is similar in purpose to NULL, except that is not a null pointer value. You can use it to initialize  
+an optional<T> instance, which has the same effect of a default constructor, and you can assign it which has the 
+effect of reseting the optional<T> instance. You can also use it in relational operators to make the predicate expression
+more clear.
    
+
    Here are some typical examples:
    
+
    +#include "boost/optional/optional.hpp" // boost/none.hpp is included automatically
+
+boost::optional<int> foo ( int a )
+{
+  return some_condition(a) ? boost::make_optional(a) : boost::none ;  
+  
+  // NOTE: in real code you can just use this: make_optional(some_condition(a), a ) 
+}
+
+boost::optional<int> opt = boost::none ;
+
+if ( opt == boost::none )
+  opt = foo(123);
+
+opt = boost::none ;
+
 
    
-
    What does the assignment do?
    
-If 'a' is uninitialized, the answer is clear: it binds to 'x' (we now have 
-another reference to 'x').
    
-But what if 'a' is already initialized? it would change the value of the 
-referenced object (whatever that is); which is inconsistent with the other 
-possible case.
    
-
    If optional<T&> would assign just like T& does, you would never be able to 
-use Optional's assignment without explicitly handling the previous 
-initialization state unless your code is capable of functioning whether after 
-the assignment, 'a' 
-aliases the same object as 'b' or not.
    
-
    That is, you would have to discriminate in order to be consistency.
    
-
    
-If in your code rebinding to another object is not an option, then is very 
-likely that binding for the fist time isn't either. In such case, assignment to 
-an uninitialized optional<T&> shall be prohibited. It is quite 
-possible that in such scenario the precondition that the lvalue must be already 
-initialized exist. If it doesn't, then binding for the first time is OK while 
-rebinding is not which is IMO 
-very unlikely.
    
-In such scenario, you can assign the value itself directly, as in:
    
-
    assert(!!opt);
-*opt=value;  
    
 
 
    
 
@@ -1506,9 +1678,8 @@ public:
 the maybe state represents a valid value, unlike the corresponding state
 of an uninitialized optional<bool>.
    
 It should be carefully considered if an optional<bool> instead of a tribool is really needed
    
-
    Second, optional<> provides an implicit conversion to bool. This conversion
-  refers to the initialization state and not to the contained value.
    
-Using optional<bool> can lead to subtle errors due to the implicit bool conversion:
    
+
    Second, optional<> provides a simple way to test initialization state: an implicit conversion to a type that evaluates as a 'bool' in a boolean context.
    
+Using optional<bool> can lead to subtle errors due to this implicit conversion:
    
 
    void foo ( bool v ) ;
 void bar()
 {
@@ -1524,7 +1695,9 @@ void bar()
 integral promotions don't apply (i.e. if foo() takes an 'int' instead, it won't compile). 
    
 
 
    Exception Safety Guarantees
    
-
    Assignment and Reset:
    
+
+
    Assignment:
    
+
    IMPORTANT NOTE: This changed in 1.33.1 with respect to previous versions
    
 
    Because of the current implementation (see Implementation Notes), all
 of the assignment methods:
    
 
      
@@ -1537,60 +1710,17 @@ of the assignment methods:
      
   InPlaceFactory const& ) 
   
    •  template<class TypedInPlaceFactory> optional<T>::operator= (
   TypedInPlaceFactory const& ) 
      • 
-  
    •  optional<T>:::reset ( T const&)
      • 
 
    
-
    Can only guarantee the basic exception safety: The lvalue optional is left uninitialized if an exception is thrown (any previous value is first destroyed using T::~T())
    
+
    cannot offer any exception safety guarantee beyond that provided by T::operator=( T const& )
    
 
    On the other hand, the uninitializing methods:
    
 
      
   
    • optional<T>::operator= ( detail::none_t ) 
      • 
-  
    • optional<T>::reset()
      • 
 
    
-
    Provide the no-throw guarantee (assuming a no-throw T::~T())
    
-
    However, since optional<> itself doesn't throw any exceptions,
-the only source for exceptions here are T's constructor, so if you know the exception guarantees
-for T::T ( T const& ), you know that optional's assignment and reset has the same guarantees.
    
-
    //
-// Case 1: Exception thrown during assignment.
-//
-T v0(123);
-optional<T> opt0(v0);
-try
-{
-  T v1(456);
-  optional<T> opt1(v1);
-  opt0 = opt1 ;
+
    Provides the no-throw guarantee (assuming a no-throw T::~T()) becuse it only destroys the stored object.
    
 
-  // If no exception was thrown, assignment succeeded.
-  assert( *opt0 == v1 ) ;
-}
-catch(...)
-{
-  // If any exception was thrown, 'opt0' is reset to uninitialized.
-  assert( !opt0 ) ;
-}
-
-//
-// Case 2: Exception thrown during reset(v)
-//
-T v0(123);
-optional<T> opt(v0);
-try
-{
-  T v1(456);
-  opt.reset ( v1 ) ;
-
-  // If no exception was thrown, reset succeeded.
-  assert( *opt == v1 ) ;
-}
-catch(...)
-{
-  // If any exception was thrown, 'opt' is reset to uninitialized.
-  assert( !opt ) ;
-}
-
    
 
    Swap:
    
 
    void swap( optional<T>&, optional<T>& ) has the same exception guarantee as swap(T&,T&) when both optionals are initialized.
    
-If only one of the optionals is initialized, it gives the same basic exception guarantee as optional<T>::reset( T const& ) (since optional<T>::reset() doesn't throw).
    
+If only one of the optionals is initialized, it gives the same exception guarantee as T::operator=( T const& ) (since optional<T>::operator=( none_t ) doesn't throw).
    
 If none of the optionals is initialized, it has no-throw guarantee since it is a no-op. 
    
 
 
    
@@ -1604,14 +1734,11 @@ T is not required to be Implementation Notes
 
    optional<T> is currently implemented
-  using a custom aligned storage facility built from alignment_of and type_with_alignment (both from Type Traits).
-  It uses a separate boolean flag to indicate the initialization state.
    
-  Placement new with T's copy constructor and T's destructor
-  are explicitly used to initialize,copy and destroy optional values.
    
-  As a result, T's default constructor is effectively by-passed, but the exception
-  guarantees are basic.
    
-  It is planned to replace the current implementation with another with
-  stronger exception safety, such as a future boost::variant. 
    
+  using a custom aligned storage facility built from alignment_of and type_with_alignment (both from Type Traits). 
+  It uses a separate boolean flag to indicate the initialization state.
    
+
    Placement new with T's copy constructor and T's destructor
+  is explicitly used to initialize and destroy optional values. This allows T's default constructor to be effectively by-passed.
    
+
    If assignment is used and the lvalue optional is uninitialized, T's copy constructor is used. However, if it is already initialized, T's assignment operator is used. This prevents optional from offering any exception guarantee stronger than the one offered by the type T itself
    
 
 
    
 
@@ -1665,12 +1792,12 @@ T is not required to be LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)
    
 
    Developed by Fernando Cacciola,
 the latest version of this file can be found at www.boost.org, and the boost discussion lists
    
 
    
-
+
\ No newline at end of file
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index d20cd84..16d4f3c 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -22,11 +22,9 @@ import testing ;
     [ run optional_test_inplace.cpp ]
     [ run optional_test_io.cpp ]
     [ compile-fail optional_test_fail1.cpp ]
-    [ compile-fail optional_test_fail2.cpp ]
     [ compile-fail optional_test_fail3a.cpp ]
     [ compile-fail optional_test_fail3b.cpp ]
     [ compile-fail optional_test_ref_fail1.cpp ]
-    [ compile-fail optional_test_ref_fail2.cpp ]
     [ compile-fail optional_test_ref_fail3.cpp ]
     [ compile-fail optional_test_ref_fail4.cpp ]
     [ compile-fail optional_test_inplace_fail.cpp ]
diff --git a/test/optional_test.cpp b/test/optional_test.cpp
index 5c10eed..02ed181 100644
--- a/test/optional_test.cpp
+++ b/test/optional_test.cpp
@@ -704,16 +704,16 @@ void test_relops( T const* )
 {
   TRACE( std::endl << BOOST_CURRENT_FUNCTION   );
 
-  T v0(18);
-  T v1(19);
-  T v2(19);
+  T v0(0);
+  T v1(1);
+  T v2(1);
 
   optional def0 ;
   optional def1 ;
   optional opt0(v0);
   optional opt1(v1);
   optional opt2(v2);
-
+  
   // Check identity
   BOOST_CHECK ( def0 == def0 ) ;
   BOOST_CHECK ( opt0 == opt0 ) ;
@@ -751,6 +751,33 @@ void test_relops( T const* )
   BOOST_CHECK ( opt1 >  opt0 ) ;
   BOOST_CHECK ( opt1 <= opt2 ) ;
   BOOST_CHECK ( opt1 >= opt0 ) ;
+  
+  // Compare against a value directly
+  BOOST_CHECK ( opt0 == v0 ) ;
+  BOOST_CHECK ( opt0 != v1 ) ;
+  BOOST_CHECK ( opt1 == v2 ) ;
+  BOOST_CHECK ( opt0 <  v1 ) ;
+  BOOST_CHECK ( opt1 >  v0 ) ;
+  BOOST_CHECK ( opt1 <= v2 ) ;
+  BOOST_CHECK ( opt1 >= v0 ) ;
+  BOOST_CHECK ( v0 != opt1 ) ;
+  BOOST_CHECK ( v1 == opt2 ) ;
+  BOOST_CHECK ( v0 <  opt1 ) ;
+  BOOST_CHECK ( v1 >  opt0 ) ;
+  BOOST_CHECK ( v1 <= opt2 ) ;
+  BOOST_CHECK ( v1 >= opt0 ) ;
+  BOOST_CHECK (   def0 != v0  ) ;
+  BOOST_CHECK ( !(def0 == v0) ) ;
+  BOOST_CHECK (   def0 <  v0  ) ;
+  BOOST_CHECK ( !(def0 >  v0) ) ;
+  BOOST_CHECK (   def0 <= v0  ) ;
+  BOOST_CHECK ( !(def0 >= v0) ) ;
+  BOOST_CHECK (   v0 != def0  ) ;
+  BOOST_CHECK ( !(v0 == def0) ) ;
+  BOOST_CHECK ( !(v0 <  def0) ) ;
+  BOOST_CHECK (   v0 >  def0  ) ;
+  BOOST_CHECK ( !(v0 <= def0) ) ;
+  BOOST_CHECK (   v0 >= opt0  ) ;
 }
 
 template
@@ -767,6 +794,10 @@ void test_none( T const* )
   BOOST_CHECK ( def0    == none ) ;
   BOOST_CHECK ( non_def != none ) ;
   BOOST_CHECK ( !def1           ) ;
+  BOOST_CHECK ( !(non_def <  none) ) ; 
+  BOOST_CHECK (   non_def >  none  ) ;
+  BOOST_CHECK ( !(non_def <= none) ) ;
+  BOOST_CHECK (   non_def >= none  ) ;
 
   non_def = none ;
   BOOST_CHECK ( !non_def ) ;
@@ -774,6 +805,24 @@ void test_none( T const* )
   test_default_implicit_construction(T(1),none);
 }
 
+template
+void test_arrow( T const* )
+{
+  TRACE( std::endl << BOOST_CURRENT_FUNCTION   );
+
+  T a(1234);
+
+  optional        oa(a) ;
+  optional const coa(a) ;
+  
+  BOOST_CHECK ( coa->V() == 1234 ) ;
+  
+  oa->V() = 4321 ;
+  
+  BOOST_CHECK (     a.V() = 1234 ) ;
+  BOOST_CHECK ( (*oa).V() = 4321 ) ;
+}
+
 void test_with_builtin_types()
 {
   TRACE( std::endl << BOOST_CURRENT_FUNCTION   );
@@ -804,6 +853,7 @@ void test_with_class_type()
   test_throwing_swap( ARG(X) );
   test_relops( ARG(X) ) ;
   test_none( ARG(X) ) ;
+  test_arrow( ARG(X) ) ;
   BOOST_CHECK ( X::count == 0 ) ;
 }
 
diff --git a/test/optional_test_ref.cpp b/test/optional_test_ref.cpp
index 1ccaeb4..91149ba 100644
--- a/test/optional_test_ref.cpp
+++ b/test/optional_test_ref.cpp
@@ -299,6 +299,23 @@ void test_none( T const* )
   BOOST_CHECK ( !non_def ) ;
 }
 
+template
+void test_arrow( T const* )
+{
+  TRACE( std::endl << BOOST_CURRENT_FUNCTION   );
+
+  T a(1234);
+
+  optional        oa(a) ;
+  optional const coa(a) ;
+  
+  BOOST_CHECK ( coa->V() == 1234 ) ;
+  
+  oa->V() = 4321 ;
+  
+  BOOST_CHECK ( a.V() = 4321 ) ;
+}
+
 void test_with_builtin_types()
 {
   TRACE( std::endl << BOOST_CURRENT_FUNCTION   );
@@ -315,6 +332,7 @@ void test_with_class_type()
   test_basics( ARG(X) );
   test_relops( ARG(X) ) ;
   test_none  ( ARG(X) ) ;
+  test_arrow ( ARG(X) ) ;
 
   BOOST_CHECK ( X::count == 0 ) ;
 }
diff --git a/test/optional_test_ref_fail2.cpp b/test/optional_test_ref_fail2.cpp
deleted file mode 100644
index 732c995..0000000
--- a/test/optional_test_ref_fail2.cpp
+++ /dev/null
@@ -1,23 +0,0 @@
-// Copyright (C) 2003, Fernando Luis Cacciola Carballal.
-//
-// Use, modification, and distribution is subject to the Boost Software
-// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
-// http://www.boost.org/LICENSE_1_0.txt)
-//
-// See http://www.boost.org/lib/optional for documentation.
-//
-// You are welcome to contact the author at:
-//  fernando_cacciola@hotmail.com
-//
-#include "boost/optional.hpp"
-
-//
-// THIS TEST SHOULD FAIL TO COMPILE
-//
-void optional_reference__test_no_ptr_access()
-{
-  boost::optional opt ;
-  opt.get_ptr();
-}
-
-

From 3499d477dcce68d7b055c9a7e4a162336b57029a Mon Sep 17 00:00:00 2001
From: Fernando Cacciola 
Date: Fri, 2 Nov 2007 22:56:23 +0000
Subject: [PATCH 02/18] Merged changests from RC_1_34_0 - base rev 33417

[SVN r40705]
---
 include/boost/optional/optional.hpp | 133 ++++++++++++++++++++++++----
 1 file changed, 115 insertions(+), 18 deletions(-)

diff --git a/include/boost/optional/optional.hpp b/include/boost/optional/optional.hpp
index 8a78a40..42277ba 100644
--- a/include/boost/optional/optional.hpp
+++ b/include/boost/optional/optional.hpp
@@ -26,7 +26,7 @@
 #include "boost/mpl/bool.hpp"
 #include "boost/mpl/not.hpp"
 #include "boost/detail/reference_content.hpp"
-#include "boost/none_t.hpp"
+#include "boost/none.hpp"
 #include "boost/utility/compare_pointees.hpp"
 
 #include "boost/optional/optional_fwd.hpp"
@@ -76,6 +76,19 @@
 #define BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION
 #endif
 
+// Daniel Wallin discovered that bind/apply.hpp badly interacts with the apply<>
+// member template of a factory as used in the optional<> implementation.
+// He proposed this simple fix which is to move the call to apply<> outside
+// namespace boost.
+namespace boost_optional_detail
+{
+  template 
+  void construct(Factory const& factory, void* address)
+  {
+    factory.BOOST_NESTED_TEMPLATE apply(address);
+  }
+}
+
 
 namespace boost {
 
@@ -173,7 +186,7 @@ class optional_base : public optional_tag
 
     // Creates an optional uninitialized.
     // No-throw
-    optional_base ( none_t const& )
+    optional_base ( none_t )
       :
       m_initialized(false) {}
 
@@ -266,7 +279,7 @@ class optional_base : public optional_tag
 
     // Assigns from "none", destroying the current value, if any, leaving this UNINITIALIZED
     // No-throw (assuming T::~T() doesn't)
-    void assign ( none_t const& ) { destroy(); }
+    void assign ( none_t ) { destroy(); }
 
 #ifndef BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
     template
@@ -309,7 +322,7 @@ class optional_base : public optional_tag
     void construct ( Expr const& factory, in_place_factory_base const* )
      {
        BOOST_STATIC_ASSERT ( ::boost::mpl::not_::value ) ;
-       factory.BOOST_NESTED_TEMPLATE apply(m_storage.address()) ;
+       boost_optional_detail::construct(factory, m_storage.address());
        m_initialized = true ;
      }
 
@@ -428,6 +441,8 @@ class optional_base : public optional_tag
     // the following olverloads are used to filter out the case and guarantee an error in case of T being a reference.
     pointer_const_type cast_ptr( internal_type const* p, is_not_reference_tag ) const { return p ; }
     pointer_type       cast_ptr( internal_type *      p, is_not_reference_tag )       { return p ; }
+    pointer_const_type cast_ptr( internal_type const* p, is_reference_tag     ) const { return &p->get() ; }
+    pointer_type       cast_ptr( internal_type *      p, is_reference_tag     )       { return &p->get() ; }
 
     bool m_initialized ;
     storage_type m_storage ;
@@ -459,7 +474,7 @@ class optional : public optional_detail::optional_base
 
     // Creates an optional uninitialized.
     // No-throw
-    optional( none_t const& none_ ) : base(none_) {}
+    optional( none_t none_ ) : base(none_) {}
 
     // Creates an optional initialized with 'val'.
     // Can throw if T::T(T const&) does
@@ -550,7 +565,7 @@ class optional : public optional_detail::optional_base
     // Assigns from a "none"
     // Which destroys the current value, if any, leaving this UNINITIALIZED
     // No-throw (assuming T::~T() doesn't)
-    optional& operator= ( none_t const& none_ )
+    optional& operator= ( none_t none_ )
       {
         this->assign( none_ ) ;
         return *this ;
@@ -678,6 +693,11 @@ get_pointer ( optional& opt )
 // optional's relational operators ( ==, !=, <, >, <=, >= ) have deep-semantics (compare values).
 // WARNING: This is UNLIKE pointers. Use equal_pointees()/less_pointess() in generic code instead.
 
+
+//
+// optional vs optional cases
+//
+
 template
 inline
 bool operator == ( optional const& x, optional const& y )
@@ -708,64 +728,141 @@ inline
 bool operator >= ( optional const& x, optional const& y )
 { return !( x < y ) ; }
 
+
+//
+// optional vs T cases
+//
 template
 inline
-bool operator == ( optional const& x, none_t const& )
+bool operator == ( optional const& x, T const& y )
+{ return equal_pointees(x, optional(y)); }
+
+template
+inline
+bool operator < ( optional const& x, T const& y )
+{ return less_pointees(x, optional(y)); }
+
+template
+inline
+bool operator != ( optional const& x, T const& y )
+{ return !( x == y ) ; }
+
+template
+inline
+bool operator > ( optional const& x, T const& y )
+{ return y < x ; }
+
+template
+inline
+bool operator <= ( optional const& x, T const& y )
+{ return !( y < x ) ; }
+
+template
+inline
+bool operator >= ( optional const& x, T const& y )
+{ return !( x < y ) ; }
+
+//
+// T vs optional cases
+//
+
+template
+inline
+bool operator == ( T const& x, optional const& y )
+{ return equal_pointees( optional(x), y ); }
+
+template
+inline
+bool operator < ( T const& x, optional const& y )
+{ return less_pointees( optional(x), y ); }
+
+template
+inline
+bool operator != ( T const& x, optional const& y )
+{ return !( x == y ) ; }
+
+template
+inline
+bool operator > ( T const& x, optional const& y )
+{ return y < x ; }
+
+template
+inline
+bool operator <= ( T const& x, optional const& y )
+{ return !( y < x ) ; }
+
+template
+inline
+bool operator >= ( T const& x, optional const& y )
+{ return !( x < y ) ; }
+
+
+//
+// optional vs none cases
+//
+
+template
+inline
+bool operator == ( optional const& x, none_t )
 { return equal_pointees(x, optional() ); }
 
 template
 inline
-bool operator < ( optional const& x, none_t const& )
+bool operator < ( optional const& x, none_t )
 { return less_pointees(x,optional() ); }
 
 template
 inline
-bool operator != ( optional const& x, none_t const& y )
+bool operator != ( optional const& x, none_t y )
 { return !( x == y ) ; }
 
 template
 inline
-bool operator > ( optional const& x, none_t const& y )
+bool operator > ( optional const& x, none_t y )
 { return y < x ; }
 
 template
 inline
-bool operator <= ( optional const& x, none_t const& y )
+bool operator <= ( optional const& x, none_t y )
 { return !( y < x ) ; }
 
 template
 inline
-bool operator >= ( optional const& x, none_t const& y )
+bool operator >= ( optional const& x, none_t y )
 { return !( x < y ) ; }
 
+//
+// none vs optional cases
+//
+
 template
 inline
-bool operator == ( none_t const& x, optional const& y )
+bool operator == ( none_t x, optional const& y )
 { return equal_pointees(optional() ,y); }
 
 template
 inline
-bool operator < ( none_t const& x, optional const& y )
+bool operator < ( none_t x, optional const& y )
 { return less_pointees(optional() ,y); }
 
 template
 inline
-bool operator != ( none_t const& x, optional const& y )
+bool operator != ( none_t x, optional const& y )
 { return !( x == y ) ; }
 
 template
 inline
-bool operator > ( none_t const& x, optional const& y )
+bool operator > ( none_t x, optional const& y )
 { return y < x ; }
 
 template
 inline
-bool operator <= ( none_t const& x, optional const& y )
+bool operator <= ( none_t x, optional const& y )
 { return !( y < x ) ; }
 
 template
 inline
-bool operator >= ( none_t const& x, optional const& y )
+bool operator >= ( none_t x, optional const& y )
 { return !( x < y ) ; }
 
 //

From 06ba35cd42e87475a57a8d0290060f1b27248401 Mon Sep 17 00:00:00 2001
From: Fernando Cacciola 
Date: Fri, 2 Nov 2007 23:06:42 +0000
Subject: [PATCH 03/18] Fixed error reported by Edward Diener

[SVN r40706]
---
 doc/optional.html | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/doc/optional.html b/doc/optional.html
index e216db5..b9ef36b 100644
--- a/doc/optional.html
+++ b/doc/optional.html
@@ -331,9 +331,9 @@ class optional
 
     template<class U> explicit optional ( optional<U> const& rhs ) ;
 
-    template<class InPlaceFactory> explicit optional ( InPlaceFactory const& f ) ;
+    template<InPlaceFactory> explicit optional ( InPlaceFactory const& f ) ;
 
-    template<class TypedInPlaceFactory> explicit optional ( TypedInPlaceFactory const& f ) ;
+    template<TypedInPlaceFactory> explicit optional ( TypedInPlaceFactory const& f ) ;
 
     optional& operator = ( none_t ) ;
 
@@ -343,9 +343,9 @@ class optional
 
     template<class U> optional& operator = ( optional<U> const& rhs ) ;
 
-    template<class InPlaceFactory> optional& operator = ( InPlaceFactory const& f ) ;
+    template<InPlaceFactory> optional& operator = ( InPlaceFactory const& f ) ;
 
-    template<class TypedInPlaceFactory> optional& operator = ( TypedInPlaceFactory const& f ) ;
+    template<TypedInPlaceFactory> optional& operator = ( TypedInPlaceFactory const& f ) ;
 
     T const& get() const ;
     T&       get() ;

From 3b5b5d82a02f14feef7bb970c0728aa56d41f3de Mon Sep 17 00:00:00 2001
From: Fernando Cacciola 
Date: Fri, 2 Nov 2007 23:41:37 +0000
Subject: [PATCH 04/18] Added test to ensure proper binding of optional
 references (in reference to Ticket 1301)

[SVN r40707]
---
 test/optional_test_ref.cpp | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/test/optional_test_ref.cpp b/test/optional_test_ref.cpp
index 91149ba..2e7f3bf 100644
--- a/test/optional_test_ref.cpp
+++ b/test/optional_test_ref.cpp
@@ -337,12 +337,30 @@ void test_with_class_type()
   BOOST_CHECK ( X::count == 0 ) ;
 }
 
+void test_binding()
+{
+  int i = 0 ;
+  optional ori1 = i ;
+  BOOST_CHECK(  &(*ori1) == &i ) ;
+	
+  optional ori2(i) ;
+  BOOST_CHECK(  &(*ori2) == &i ) ;
+	
+  int const ci = 0 ;
+  optional orci1 = ci ;
+  BOOST_CHECK(  &(*orci1) == &ci ) ;
+	
+  optional orci2 = ci ;
+  BOOST_CHECK(  &(*orci2) == &ci ) ;
+}
+
 int test_main( int, char* [] )
 {
   try
   {
     test_with_class_type();
     test_with_builtin_types();
+		test_binding();
   }
   catch ( ... )
   {

From 05a685b035159a0649187a26bd323deed623ebd6 Mon Sep 17 00:00:00 2001
From: Fernando Cacciola 
Date: Tue, 6 Nov 2007 22:21:43 +0000
Subject: [PATCH 05/18] Fixed intention in the added binding test

[SVN r40860]
---
 test/optional_test_ref.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/optional_test_ref.cpp b/test/optional_test_ref.cpp
index 2e7f3bf..08ee87e 100644
--- a/test/optional_test_ref.cpp
+++ b/test/optional_test_ref.cpp
@@ -350,7 +350,7 @@ void test_binding()
   optional orci1 = ci ;
   BOOST_CHECK(  &(*orci1) == &ci ) ;
 	
-  optional orci2 = ci ;
+  optional orci2(ci) ;
   BOOST_CHECK(  &(*orci2) == &ci ) ;
 }
 

From f6518df0c4fe924f73761d579f0fba23a449a6b2 Mon Sep 17 00:00:00 2001
From: Beman Dawes 
Date: Thu, 15 Nov 2007 15:20:27 +0000
Subject: [PATCH 06/18] Get rid of .cvsignore files

[SVN r41107]
---
 test/.cvsignore | 1 -
 1 file changed, 1 deletion(-)
 delete mode 100644 test/.cvsignore

diff --git a/test/.cvsignore b/test/.cvsignore
deleted file mode 100644
index ba077a4..0000000
--- a/test/.cvsignore
+++ /dev/null
@@ -1 +0,0 @@
-bin

From 9afdbe65e70e2d0308abe0575d6585885769b62c Mon Sep 17 00:00:00 2001
From: Beman Dawes 
Date: Sat, 17 Nov 2007 20:13:16 +0000
Subject: [PATCH 07/18] // Add or correct comment identifying Boost library
 this header is associated with.

[SVN r41173]
---
 include/boost/none.hpp     | 2 +-
 include/boost/none_t.hpp   | 2 +-
 include/boost/optional.hpp | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/boost/none.hpp b/include/boost/none.hpp
index b0e94a2..bd342da 100644
--- a/include/boost/none.hpp
+++ b/include/boost/none.hpp
@@ -4,7 +4,7 @@
 // (See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt)
 //
-// See http://www.boost.org/lib/optional/ for documentation.
+// See http://www.boost.org/libs/optional for documentation.
 //
 // You are welcome to contact the author at:
 //  fernando_cacciola@hotmail.com
diff --git a/include/boost/none_t.hpp b/include/boost/none_t.hpp
index 4b97e20..63ad926 100644
--- a/include/boost/none_t.hpp
+++ b/include/boost/none_t.hpp
@@ -4,7 +4,7 @@
 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt)
 //
-// See http://www.boost.org/lib/optional for documentation.
+// See http://www.boost.org/libs/optional for documentation.
 //
 // You are welcome to contact the author at:
 //  fernando_cacciola@hotmail.com
diff --git a/include/boost/optional.hpp b/include/boost/optional.hpp
index bc5c5d3..40cf12e 100644
--- a/include/boost/optional.hpp
+++ b/include/boost/optional.hpp
@@ -4,7 +4,7 @@
 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt)
 //
-// See http://www.boost.org/lib/optional for documentation.
+// See http://www.boost.org/libs/optional for documentation.
 //
 // You are welcome to contact the author at:
 //  fernando_cacciola@hotmail.com

From 95c864e119314a2611f283a040294c7c8a234d90 Mon Sep 17 00:00:00 2001
From: Fernando Cacciola 
Date: Sun, 25 Nov 2007 20:26:14 +0000
Subject: [PATCH 08/18] Cast to base added to avoid a call to the convertir
 constructor/assignment (see Tickes 1419 and 1420)

[SVN r41381]
---
 include/boost/optional/optional.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/boost/optional/optional.hpp b/include/boost/optional/optional.hpp
index 42277ba..ebcf17a 100644
--- a/include/boost/optional/optional.hpp
+++ b/include/boost/optional/optional.hpp
@@ -516,7 +516,7 @@ class optional : public optional_detail::optional_base
 
     // Creates a deep copy of another optional
     // Can throw if T::T(T const&) does
-    optional ( optional const& rhs ) : base(rhs) {}
+    optional ( optional const& rhs ) : base( static_cast(rhs) ) {}
 
    // No-throw (assuming T::~T() doesn't)
     ~optional() {}
@@ -550,7 +550,7 @@ class optional : public optional_detail::optional_base
     //  (NOTE: On BCB, this operator is not actually called and left is left UNMODIFIED in case of a throw)
     optional& operator= ( optional const& rhs )
       {
-        this->assign( rhs ) ;
+        this->assign( static_cast(rhs) ) ;
         return *this ;
       }
 

From 3e33d4a200c9654e80e0349f7645d46345107c3b Mon Sep 17 00:00:00 2001
From: Matias Capeletto 
Date: Thu, 14 Feb 2008 17:43:52 +0000
Subject: [PATCH 09/18] optional docs fixes

[SVN r43247]
---
 doc/Jamfile.v2                                |    6 +-
 .../a_note_about_optional_bool_.html          |   26 +-
 doc/html/boost_optional/acknowledgments.html  |   30 +-
 .../dependencies_and_portability.html         |   26 +-
 .../boost_optional/detailed_semantics.html    |   74 +-
 doc/html/boost_optional/development.html      |   45 +-
 doc/html/boost_optional/examples.html         |   26 +-
 .../exception_safety_guarantees.html          |   28 +-
 .../boost_optional/implementation_notes.html  |   26 +-
 .../boost_optional/in_place_factories.html    |   26 +-
 .../boost_optional/optional_references.html   |   26 +-
 ...for_assignment_of_optional_references.html |   28 +-
 doc/html/boost_optional/synopsis.html         |   26 +-
 .../boost_optional/type_requirements.html     |   26 +-
 doc/html/images/callouts/1.png                |  Bin 391 -> 0 bytes
 doc/html/images/callouts/10.png               |  Bin 485 -> 0 bytes
 doc/html/images/callouts/11.png               |  Bin 410 -> 0 bytes
 doc/html/images/callouts/12.png               |  Bin 488 -> 0 bytes
 doc/html/images/callouts/13.png               |  Bin 509 -> 0 bytes
 doc/html/images/callouts/14.png               |  Bin 499 -> 0 bytes
 doc/html/images/callouts/15.png               |  Bin 507 -> 0 bytes
 doc/html/images/callouts/2.png                |  Bin 446 -> 0 bytes
 doc/html/images/callouts/3.png                |  Bin 431 -> 0 bytes
 doc/html/images/callouts/4.png                |  Bin 441 -> 0 bytes
 doc/html/images/callouts/5.png                |  Bin 423 -> 0 bytes
 doc/html/images/callouts/6.png                |  Bin 431 -> 0 bytes
 doc/html/images/callouts/7.png                |  Bin 397 -> 0 bytes
 doc/html/images/callouts/8.png                |  Bin 434 -> 0 bytes
 doc/html/images/callouts/9.png                |  Bin 420 -> 0 bytes
 doc/html/images/caution.png                   |  Bin 4286 -> 0 bytes
 doc/html/images/home.png                      |  Bin 1105 -> 0 bytes
 doc/html/images/important.png                 |  Bin 4666 -> 0 bytes
 doc/html/images/next.png                      |  Bin 768 -> 0 bytes
 doc/html/images/note.png                      |  Bin 4648 -> 0 bytes
 doc/html/images/prev.png                      |  Bin 741 -> 0 bytes
 doc/html/images/tip.png                       |  Bin 3902 -> 0 bytes
 doc/html/images/up.png                        |  Bin 766 -> 0 bytes
 doc/html/images/warning.png                   |  Bin 3927 -> 0 bytes
 doc/html/index.html                           |   41 +-
 doc/optional.html                             | 1803 -----------------
 doc/optional.qbk                              |    5 -
 doc/reference.qbk                             |    1 +
 42 files changed, 265 insertions(+), 2004 deletions(-)
 delete mode 100644 doc/html/images/callouts/1.png
 delete mode 100644 doc/html/images/callouts/10.png
 delete mode 100644 doc/html/images/callouts/11.png
 delete mode 100644 doc/html/images/callouts/12.png
 delete mode 100644 doc/html/images/callouts/13.png
 delete mode 100644 doc/html/images/callouts/14.png
 delete mode 100644 doc/html/images/callouts/15.png
 delete mode 100644 doc/html/images/callouts/2.png
 delete mode 100644 doc/html/images/callouts/3.png
 delete mode 100644 doc/html/images/callouts/4.png
 delete mode 100644 doc/html/images/callouts/5.png
 delete mode 100644 doc/html/images/callouts/6.png
 delete mode 100644 doc/html/images/callouts/7.png
 delete mode 100644 doc/html/images/callouts/8.png
 delete mode 100644 doc/html/images/callouts/9.png
 delete mode 100755 doc/html/images/caution.png
 delete mode 100755 doc/html/images/home.png
 delete mode 100755 doc/html/images/important.png
 delete mode 100755 doc/html/images/next.png
 delete mode 100755 doc/html/images/note.png
 delete mode 100755 doc/html/images/prev.png
 delete mode 100755 doc/html/images/tip.png
 delete mode 100755 doc/html/images/up.png
 delete mode 100755 doc/html/images/warning.png
 delete mode 100644 doc/optional.html

diff --git a/doc/Jamfile.v2 b/doc/Jamfile.v2
index 95574ce..abdaf20 100644
--- a/doc/Jamfile.v2
+++ b/doc/Jamfile.v2
@@ -21,8 +21,10 @@ boostbook standalone
     :
         optional
     :
-        toc.max.depth=1
-        toc.section.depth=1
+        boost.root=../../../..
+        boost.libraries=../../../libraries.htm
+        toc.max.depth=2
+        toc.section.depth=2
         chunk.section.depth=1
     ;
 
diff --git a/doc/html/boost_optional/a_note_about_optional_bool_.html b/doc/html/boost_optional/a_note_about_optional_bool_.html
index 42d69df..5191d1d 100644
--- a/doc/html/boost_optional/a_note_about_optional_bool_.html
+++ b/doc/html/boost_optional/a_note_about_optional_bool_.html
@@ -12,17 +12,17 @@
     Guarantees">
 
 
-
-
-
-
-
-
-
-
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
+
+
+
+
+
+
+
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-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
    
 
    
@@ -74,11 +74,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
 
diff --git a/doc/html/boost_optional/acknowledgments.html b/doc/html/boost_optional/acknowledgments.html
index e2cc05a..09e3c71 100644
--- a/doc/html/boost_optional/acknowledgments.html
+++ b/doc/html/boost_optional/acknowledgments.html
@@ -10,24 +10,24 @@
     and Portability">
 
 
-
-
-
-
-
-
-
-
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
+
+
+
+
+
+
+
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
 
    
 
    
-PrevUpHome
+PrevUpHome
 
    
 
    
 
    
 
    
-
+
       Pre-formal
       review
     
    
@@ -66,7 +66,7 @@
       
 
    
 
    
-
+
       Post-formal
       review
     
    
@@ -112,11 +112,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
-PrevUpHome
+PrevUpHome
 
    
 
 
diff --git a/doc/html/boost_optional/dependencies_and_portability.html b/doc/html/boost_optional/dependencies_and_portability.html
index ccc0d2c..35ecb80 100644
--- a/doc/html/boost_optional/dependencies_and_portability.html
+++ b/doc/html/boost_optional/dependencies_and_portability.html
@@ -11,17 +11,17 @@
 
 
 
-
-
-
-
-
-
-
-
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
+
+
+
+
+
+
+
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+PrevUpHomeNext
 
    
 
    
 
    
@@ -36,11 +36,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
 
diff --git a/doc/html/boost_optional/detailed_semantics.html b/doc/html/boost_optional/detailed_semantics.html
index bbebfd7..ef68023 100644
--- a/doc/html/boost_optional/detailed_semantics.html
+++ b/doc/html/boost_optional/detailed_semantics.html
@@ -10,17 +10,17 @@
 
 
 
-
-
-
-
-
-
-
-
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
+
+
+
+
+
+
+
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
 
    
 
    
-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
    
 
    
@@ -29,36 +29,42 @@
 
    
       Because T might be of reference
       type, in the sequel, those entries whose semantic depends on T being of reference type or not will be
-      distinguished using the following convention: * If the entry reads: optional<T(not a ref)>, the description corresponds only to the
-      case where T is not of reference
-      type. * If the entry reads: optional<T&>,
-      the description corresponds only to the case where T
-      is of reference type. * If the entry reads: optional<T>,
-      the description is the same for both cases.
+      distinguished using the following convention:
     
    
+
      
+
    • 
+        If the entry reads: optional<T(not
+        a ref)>, the description
+        corresponds only to the case where T
+        is not of reference type.
+      
      • 
+
    • 
+        If the entry reads: optional<T&>,
+        the description corresponds only to the case where T
+        is of reference type.
+      
      • 
+
    • 
+        If the entry reads: optional<T>,
+        the description is the same for both cases.
+      
      • 
+
    
 
    
-
+
-
+
    
 
    [Note][Note]
 Note
 
    
-
    
-        
    
-
    
-          The following section contains various assert() which are used only to show the postconditions
-          as sample code. It is not implied that the type T
-          must support each particular expression but that if the expression is supported,
-          the implied condition holds.
-        
    
-
    
-      
    
-
    
+        The following section contains various assert() which are used only to show the postconditions
+        as sample code. It is not implied that the type T
+        must support each particular expression but that if the expression is supported,
+        the implied condition holds.
+      
    
 
    
 
    
       space
     
    
 
    
-
+
       optional
       class member functions
     
    
@@ -1334,7 +1340,7 @@
       space
     
    
 
    
-
+
       Free functions
     
    
 
    
@@ -1693,11 +1699,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
 
diff --git a/doc/html/boost_optional/development.html b/doc/html/boost_optional/development.html
index c013432..8d58d8b 100644
--- a/doc/html/boost_optional/development.html
+++ b/doc/html/boost_optional/development.html
@@ -10,17 +10,17 @@
 
 
 
-
-
-
-
-
-
-
-
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
+
+
+
+
+
+
+
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
 
    
 
    
-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
    
 
    
@@ -292,7 +292,7 @@
         itself which are supported by a special interface.
       
    
 
    
-
+
         Lexically-hinted
         Value Access in the presence of possibly untitialized optional objects: The
         operators * and ->
@@ -357,7 +357,7 @@
         incarnated by pointers.
       
    
 
    
-
+
         Optional<T>
         as a model of OptionalPointee
       
    
@@ -369,19 +369,12 @@
       
    
 
    
-
+
-
+
    
 
    [Warning][Warning]
 Warning
 
    
-
    
-          
    
-
    
-            However, it is particularly important to note that optional<> objects are not pointers. optional<> is not, and does not model, a
-            pointer.
-          
    
-
    
-        
    
-
    
+          However, it is particularly important to note that optional<> objects are not pointers. optional<> is not, and does not model, a pointer.
+        
    
 
    
 
    
         For instance, optional<>
@@ -405,11 +398,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
 
diff --git a/doc/html/boost_optional/examples.html b/doc/html/boost_optional/examples.html
index 7fdb8c8..7685a73 100644
--- a/doc/html/boost_optional/examples.html
+++ b/doc/html/boost_optional/examples.html
@@ -10,17 +10,17 @@
 
 
 
-
-
-
-
-
-
-
-
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
+
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+
+
+
+
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+PrevUpHomeNext
 
    
 
    
 
    
@@ -141,11 +141,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
 
diff --git a/doc/html/boost_optional/exception_safety_guarantees.html b/doc/html/boost_optional/exception_safety_guarantees.html
index 6b4ab64..8f6504f 100644
--- a/doc/html/boost_optional/exception_safety_guarantees.html
+++ b/doc/html/boost_optional/exception_safety_guarantees.html
@@ -12,17 +12,17 @@
 
 
 
-
-
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-
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-
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-
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
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+
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+
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+PrevUpHomeNext
 
    
 
    
 
    
@@ -116,7 +116,7 @@
 }
 
    
 
    
-
+
       Swap
     
    
 
    
@@ -130,11 +130,15 @@
 
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
-PrevUpHomeNext
+PrevUpHomeNext
 
    
 
 
diff --git a/doc/html/boost_optional/implementation_notes.html b/doc/html/boost_optional/implementation_notes.html
index 54af9ab..c0225b3 100644
--- a/doc/html/boost_optional/implementation_notes.html
+++ b/doc/html/boost_optional/implementation_notes.html
@@ -11,17 +11,17 @@
     and Portability">
 
 
-
-
-
-
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-
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    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
+
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+PrevUpHomeNext
 
    
 
    
 
    
@@ -42,11 +42,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
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+PrevUpHomeNext
 
    
 
 
diff --git a/doc/html/boost_optional/in_place_factories.html b/doc/html/boost_optional/in_place_factories.html
index be2ccbf..a972384 100644
--- a/doc/html/boost_optional/in_place_factories.html
+++ b/doc/html/boost_optional/in_place_factories.html
@@ -12,17 +12,17 @@
     optional<bool>">
 
 
-
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@@ -190,11 +190,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
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diff --git a/doc/html/boost_optional/optional_references.html b/doc/html/boost_optional/optional_references.html
index 396dff0..1222a42 100644
--- a/doc/html/boost_optional/optional_references.html
+++ b/doc/html/boost_optional/optional_references.html
@@ -11,17 +11,17 @@
     semantics for assignment of optional references">
 
 
-
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@@ -72,11 +72,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
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diff --git a/doc/html/boost_optional/rebinding_semantics_for_assignment_of_optional_references.html b/doc/html/boost_optional/rebinding_semantics_for_assignment_of_optional_references.html
index 8906812..5b894aa 100644
--- a/doc/html/boost_optional/rebinding_semantics_for_assignment_of_optional_references.html
+++ b/doc/html/boost_optional/rebinding_semantics_for_assignment_of_optional_references.html
@@ -11,17 +11,17 @@
 
 
 
-
-
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@@ -75,7 +75,7 @@
 assert(b==3); 
 
    
 
    
-
+
       Rationale
     
    
 
    
@@ -141,11 +141,15 @@
 
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
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diff --git a/doc/html/boost_optional/synopsis.html b/doc/html/boost_optional/synopsis.html
index 198750e..c128fc6 100644
--- a/doc/html/boost_optional/synopsis.html
+++ b/doc/html/boost_optional/synopsis.html
@@ -10,17 +10,17 @@
 
 
 
-
-
-
-
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@@ -137,11 +137,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
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diff --git a/doc/html/boost_optional/type_requirements.html b/doc/html/boost_optional/type_requirements.html
index 8da1a86..0676bf1 100644
--- a/doc/html/boost_optional/type_requirements.html
+++ b/doc/html/boost_optional/type_requirements.html
@@ -11,17 +11,17 @@
 
 
 
-
-
-
-
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@@ -40,11 +40,15 @@
 
    
 
-
+
    
 Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+      
    
+
    		
 
    
 
    
 
    
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diff --git a/doc/html/images/callouts/1.png b/doc/html/images/callouts/1.png
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diff --git a/doc/html/index.html b/doc/html/index.html
index 298875d..24277e1 100644
--- a/doc/html/index.html
+++ b/doc/html/index.html
@@ -8,16 +8,16 @@
 
 
 
-
-
-
-
-
-
-
-
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
+
+
+
+
+
+
+
+
    Boost C++ LibrariesHomeLibrariesPeopleFAQMore
    
 
    
-
    Next
    
+
    Next
    
 
    
 
    
 
    
@@ -27,7 +27,7 @@
 
    
 
    Copyright © 2003 -2007 Fernando Luis Cacciola Carballal
    
 
    
-
    
+
    
         Distributed under the Boost Software License, Version 1.0. (See accompanying
         file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
       
    
@@ -38,9 +38,24 @@
 
    
 
    Motivation
    
 
    Development
    
+
    
+
    The models
    
+
    The semantics
    
+
    The Interface
    
+
    
 
    Synopsis
    
 
    Detailed Semantics
    
 
    Examples
    
+
    
+
    Optional
+      return values
    
+
    Optional
+      local variables
    
+
    Optional
+      data members
    
+
    Bypassing
+      expensive unnecessary default construction
    
+
    
 
    Optional references
    
 
    Rebinding
     semantics for assignment of optional references
    
@@ -159,10 +174,10 @@
   
    
 
    
 
-
-
+
+
    Last revised: May 29, 2007 at 06:31:03 GMT
    Last revised: February 12, 2008 at 22:47:14 GMT
    		
 
    
 
    
-
    Next
    
+
    Next
    
 
 
diff --git a/doc/optional.html b/doc/optional.html
deleted file mode 100644
index b9ef36b..0000000
--- a/doc/optional.html
+++ /dev/null
@@ -1,1803 +0,0 @@
-
-
-
-
-
-
-
-
-
-
-Header 
-
-
-
-
    Header <boost/optional/optional.hpp> 
    
-
-
    Contents
    
-
    
-  
    Motivation
    
-  
    Development
    
-  
    Synopsis
    
-  
    Semantics
    
-  
    Examples
    
-  
    Optional references
    
-  
    Rebinding semantics for assignment of optional references
    
-  
    none_t and none
    
-  
    In-Place Factories
    
-  
    A note about optional<bool>
    
-  
    Exception Safety Guarantees
    
-  
    Type requirements
    
-  
    Implementation Notes
    
-  
    Dependencies and Portability
    
-  
    Acknowledgment
    
-
    
-
-
    
-
-
    Motivation
    
-
-
    Consider these functions which should return a value but which might not have
-  a value to return:
    
-
    (A) double sqrt(double n );
-(B) char get_async_input();
-(C) point polygon::get_any_point_effectively_inside();
    
-
    There are different approaches to the issue of not having a value to return.
    
-
    A typical approach is to consider the existence of a valid return value as
-  a postcondition, so that if the function cannot compute the value to return,
-  it has either undefined behavior (and can use assert in a debug build)
-  or uses a runtime check and throws an exception if the postcondition is violated.
-  This is a reasonable choice for example, for function (A), because the
-  lack of a proper return value is directly related to an invalid parameter (out
-  of domain argument), so it is appropriate to require the callee to supply only
-  parameters in a valid domain for execution to continue normally.
    
-
    However, function (B), because of its asynchronous nature, does not fail just
-  because it can't find a value to return; so it is incorrect to consider
-  such a situation an error and assert or throw an exception. This function must
-  return, and somehow, must tell the callee that it is not returning a meaningful
-  value.
    
-
    A similar situation occurs with function (C): it is conceptually an error to
-  ask a null-area polygon to return a point inside itself, but in many
-  applications, it is just impractical for performance reasons to treat this as
-  an error (because detecting that the polygon has no area might be too expensive
-  to be required to be tested previously), and either an arbitrary point (typically
-  at infinity) is returned, or some efficient way to tell the callee that there
-  is no such point is used.
    
-
    There are various mechanisms to let functions communicate that the returned
-  value is not valid. One such mechanism, which is quite common since it has zero
-  or negligible overhead, is to use a special value which is reserved to communicate
-  this. Classical examples of such special values are EOF, string::npos, points
-  at infinity, etc...
    
-
    When those values exist, i.e. the return type can hold all meaningful values
-  plus the signal value, this mechanism is quite appropriate and
-  well known. Unfortunately, there are cases when such values do not exist. In
-  these cases, the usual alternative is either to use a wider type, such as 'int'
-  in place of 'char'; or a compound type, such as std::pair<point,bool>.
-
    
-
    Returning a std::pair<T,bool>, thus attaching a boolean flag to the result
-  which indicates if the result is meaningful, has the advantage that can be turned
-  into a consistent idiom since the first element of the pair can be whatever
-  the function would conceptually return. For example, the last two functions
-  could have the following interface:
    
-
    std::pair<char,bool> get_async_input();
-std::pair<point,bool> polygon::get_any_point_effectively_inside();
    
-
    These functions use a consistent interface for dealing with possibly inexistent
-  results:
    
-
    std::pair<point,bool> p = poly.get_any_point_effectively_inside();
-if ( p.second )
-  flood_fill(p.first);
-
    
-
-
    However, not only is this quite a burden syntactically, it is also error
-  prone since the user can easily use the function result (first element of the
-  pair) without ever checking if it has a valid value.
    
-
    Clearly, we need a better idiom.
    
-
-
    Development
    
-
-
    The models:
    
-
    In C++, we can declare an object (a variable) of type T, and we can give this variable
-  an initial value (through an initializer. (c.f. 8.5)).
    
-  When a declaration includes a non-empty initializer (an initial value is given), it is said that
-  the object has been initialized.
    
-  If the declaration uses an empty initializer (no initial value is given),
-  and neither default nor value initialization applies, it is said that the object is
-  uninitialized. Its actual value exist but has an
-  indeterminate initial value (c.f. 8.5.9).
    
-  optional<T> intends to formalize the notion of initialization 
-(or lack of it)
-  allowing a program to test whether an object has been initialized and stating that access to
-  the value of an uninitialized object is undefined behavior. That is,
-  when a variable is declared as optional<T> and no initial value is given,
-  the variable is formally uninitialized. A formally uninitialized optional object has conceptually
-  no value at all and this situation can be tested at runtime. It is formally 
-undefined behavior
-  to try to access the value of an uninitialized optional. An uninitialized optional can be assigned a      value, in which case its initialization state changes to initialized. Furthermore, given the formal
-  treatment of initialization states in optional objects, it is even possible to reset an optional to uninitialized.
    
-
    In C++ there is no formal notion of uninitialized objects, which
-  means that objects always have an initial value even if indeterminate.
    
-  As discussed on the previous section, this has a drawback because you need additional
-  information to tell if an object has been effectively initialized.
    
-  One of the typical ways in which this has been historically
-  dealt with is via a special value: EOF,npos,-1, etc... This is equivalent to adding
-  the special value to the set of possible values of a given type. This super set of
-  T plus some nil_t—were nil_t is some stateless POD-can be modeled in modern
-  languages as a discriminated union of T and nil_t.
-  Discriminated unions are often called variants. A variant has a current type,
-  which in our case is either T or nil_t.
    
-  Using the Boost.Variant library, this model can be implemented
-  in terms of boost::variant<T,nil_t>.
    
-  There is precedent for a discriminated union as a model for an optional value: the
-  Haskell Maybe built-in type constructor. 
-Thus, a discriminated union T+nil_t serves as a conceptual foundation.
    
-
    A variant<T,nil_t> follows naturally from the traditional idiom of extending
-the range of possible values adding an additional sentinel value with the special meaning of Nothing. 
-However, this additional Nothing value is largely irrelevant for our purpose
- since our goal is to formalize the notion of uninitialized objects and, while a special extended value can be used to convey that meaning, it is not strictly 
-necessary in order to do so.
    
-
    The observation made in the last paragraph about the irrelevant nature of the additional nil_t with respect to
-purpose of optional<T> suggests
-an alternative model: a container that either has a value of T or nothing.
-
    
-
    As of this writing I don't know of any precedent for a variable-size fixed-capacity (of 1)
-stack-based container model for optional values, yet I believe this is the consequence of
-the lack of practical implementations of such a container rather than an inherent shortcoming
-of the container model.
    
-
    In any event, both the discriminated-union or the single-element container models serve as a conceptual
-ground for a class representing optional—i.e. possibly uninitialized—objects.
    
-For instance, these models show the exact semantics required for a wrapper of optional values:
    
-
    Discriminated-union:
    
-
    
-
  • deep-copy semantics:  copies of the variant implies copies of the value.
    • 
-
  • deep-relational semantics: comparisons between variants matches both current types and values
    • 
-
  • If the variant's current type is T, it is modeling an initialized optional.
    • 
-
  • If the variant's current type is not T, it is modeling an uninitialized optional.
    • 
-
  • Testing if the variant's current type is T models testing if the optional is initialized
    • 
-
  • Trying to extract a T from a variant when its current type is not T, models the undefined 
-behavior
-of trying to access the value of an uninitialized optional
    • 
-
    
-
    Single-element container:
    
-
    
-
  • deep-copy semantics:  copies of the container implies copies of the value.
    • 
-
  • deep-relational semantics: comparisons between containers compare container size and if match, contained value
    • 
-
  • If the container is not empty (contains an object of type T), it is modeling an initialized optional.
    • 
-
  • If the container is empty, it is modeling an uninitialized optional.
    • 
-
  • Testing if the container is empty models testing if the optional is initialized
    • 
-
  • Trying to extract a T from an empty container models the undefined behavior
-of trying to access the value of an uninitialized optional
    • 
-
    
-
-
    The semantics:
    
-
    Objects of type optional<T> are intended to be used in places where objects of type T would
-but which might be uninitialized. Hence, optional<T>'s purpose is to formalize the
-additional possibly uninitialized state.
    
-From the perspective of this role, optional<T> can have the same operational semantics of T
-plus the additional semantics corresponding to this special state.
    
-As such, optional<T> could be thought of as a supertype of T. Of course,
-we can't do that in C++, so we need to compose the desired semantics using a different mechanism.
    
-Doing it the other way around, that is, making optional<T> a subtype of T is not only
-conceptually wrong but also impractical: it is not allowed to derive from a non-class type, such as a 
-built-in type.
    
-
-
    We can draw from the purpose of optional<T> the required basic semantics:
    
-
-
    
-
    Default Construction: To introduce a formally uninitialized wrapped
-object.
    
-
-
    Direct Value Construction via copy: To introduce a formally
-initialized wrapped object whose value is obtained as a copy of some object.
    
-
-
    Deep Copy Construction: To obtain a new yet equivalent wrapped
-object.
    
-
-
    Direct Value Assignment (upon initialized): To assign a value to the wrapped object.
    
-
-
    Direct Value Assignment (upon uninitialized): To initialize the wrapped object
-with a value obtained
-as a copy of some object.
    
-
-
    Assignment (upon initialized): To assign to the wrapped object the value 
-of another wrapped object.
    
-
-
    Assignment (upon uninitialized): To initialize the wrapped object
-with value of another wrapped object.
    
-
-
    Deep Relational Operations (when supported by the type T): To compare
-wrapped object values taking into account the presence of uninitialized
-states.
    
-
-
    Value access: To unwrap the wrapped object.
    
-
-
    Initialization state query: To determine if the object is formally
-initialized or not.
    
-
-
    Swap: To exchange wrapped objects. (with whatever exception safety
-guarantees are provided by T's swap).
    
-
-
    De-initialization: To release the wrapped object (if any) and leave
-the wrapper in the uninitialized state.
    
-
-
    
-
-
    Additional operations are useful, such as converting constructors and
-converting assignments, in-place construction and assignment, and safe value
-access via a pointer to the wrapped object or null.
    
-
    The Interface:
    
-
    Since the purpose of optional is to allow us to use objects with a formal
-uninitialized additional state, the interface could try to follow the interface
-of the underlying T type as much as possible. In order to choose the proper
-degree of adoption of the native T interface, the following must be noted: 
    
-Even if all the operations supported by an instance of type T are defined for
-the entire range of values for such a type, an optional<T> extends such a set of
-values with a new value for which most (otherwise valid) operations are not
-defined in terms of T.
    
-Furthermore, since optional<T> itself is merely a T wrapper (modeling a T
-supertype), any attempt to define such operations upon uninitialized optionals
-will be totally artificial w.r.t. T.
    
-This library chooses an interface which follows from T's interface only for
-those operations which are well defined (w.r.t the type T) even if any of the
-operands are uninitialized. These operations include: construction,
-copy-construction, assignment, swap and relational operations.
    
-For the value access operations, which are undefined (w.r.t the type T) when the
-operand is uninitialized, a different interface is chosen (which will be
-explained next).
    
-Also, the presence of the possibly uninitialized state requires additional
-operations not provided by T itself which are supported by a special interface.
    
-
    Lexically-hinted Value Access in the presence of possibly untitialized
-optional objects: The operators * and ->
    
-
    A relevant feature of a pointer is that it can have a null
-  pointer value. This is a special value which is used to indicate that the
-  pointer is not referring to any object at all. In other words, null pointer
-  values convey the notion of inexistent objects.
    
-
    This meaning of the null pointer value allowed pointers to became a de facto standard
-  for handling optional objects because all you have to do to refer to a value which you
-  don't really have is to use a null pointer value of the appropriate type.
-  Pointers have been used for decades—from the days of C APIs to modern C++ libraries—to
-  refer to optional (that is, possibly inexistent) objects; particularly
-  as optional arguments to a function, but also quite often as optional data members.
    
-
    The possible presence of a null pointer value makes the operations that access the
-  pointee's value possibly undefined, therefore, expressions which use dereference
-  and access operators, such as: ( *p = 2 ) and ( p->foo()),
-  implicitly convey the notion of optionality, and this information is tied to
-  the syntax of the expressions. That is, the presence of operators * and -> tell by
-  themselves—without any additional context—that the expression will be undefined unless
-  the implied pointee actually exist.
    
-
    Such a de facto idiom for referring to optional objects can be formalized in the form of a
-concept: the OptionalPointee concept.
    
-This concept captures the syntactic usage of operators *, -> and conversion to bool to convey
-the notion of optionality.
    
-
    However, pointers are good to refer to optional objects, but not particularly good
-to handle the optional objects in all other respects, such as initializing or moving/copying
-them. The problem resides in the shallow-copy of pointer semantics: if you need to
-  effectively move or copy the object, pointers alone are not enough. The problem
-  is that copies of pointers do not imply copies of pointees. For example, as
-  was discussed in the motivation, pointers alone cannot be used to return optional
-  objects from a function because the object must move outside from the function and
-  into the caller's context.
    
-  A solution to the shallow-copy problem that is often used is to resort to dynamic
-  allocation and use a smart pointer to automatically handle the details of this.
-  For example, if a function is to optionally return an object X, it can use shared_ptr<X>
-  as the return value. However, this requires dynamic allocation of X. If X is
-  a built-in or small POD, this technique is very poor in terms of required resources.
-  Optional objects are essentially values so it is very convenient to be able to use automatic
-  storage and deep-copy semantics to manipulate optional values just as we do with ordinary
-  values. Pointers do not have this semantics, so are inappropriate for the initialization and
-  transport of optional values, yet are quite convenient for handling the access to the
-  possible undefined value because of the idiomatic aid present in the OptionalPointee
-  concept incarnated by pointers.
-
    
-
    Optional<T> as a model of OptionalPointee
    
-
    For value access operations optional<> uses operators * and -> to lexically
-warn about the possibly uninitialized state appealing to the familiar pointer
-semantics w.r.t. to null pointers.
    
-However, it is particularly important to note that optional<> objects are not pointers. optional<>
-is not, and does not model, a pointer.
-
    For instance, optional<> does not have shallow-copy so does not alias: two different optionals
-  never refer to the same value unless T itself is a reference (but may have equivalent values).
    
-  The difference between an optional<T> and a pointer must be kept in mind, particularly
-  because the semantics of relational operators are different: since optional<T>
-  is a value-wrapper, relational operators are deep: they compare optional values;
-  but relational operators for pointers are shallow:  they do not compare pointee values.
    
-  As a result, you might be able to replace optional<T> by T* on some situations but
-  not always. Specifically, on generic code written for both, you cannot use relational
-  operators directly, and must use the template functions
-  equal_pointees() and
-  less_pointees() instead.
-
    
-
-
    Synopsis
    
-
-
    namespace boost {
-
-template<class T>
-class optional
-{
-  public :
-
-    (If T is of reference type, the parameters and results by reference are by value)
-
-    optional () ;
-
-    optional ( none_t ) ;
-
-    optional ( T const& v ) ;
-
-    optional ( bool condition, T const& v ) ;  [new in 1.34]
-    
-    optional ( optional const& rhs ) ;
-
-    template<class U> explicit optional ( optional<U> const& rhs ) ;
-
-    template<InPlaceFactory> explicit optional ( InPlaceFactory const& f ) ;
-
-    template<TypedInPlaceFactory> explicit optional ( TypedInPlaceFactory const& f ) ;
-
-    optional& operator = ( none_t ) ;
-
-    optional& operator = ( T const& v ) ;
-
-    optional& operator = ( optional const& rhs ) ;
-
-    template<class U> optional& operator = ( optional<U> const& rhs ) ;
-
-    template<InPlaceFactory> optional& operator = ( InPlaceFactory const& f ) ;
-
-    template<TypedInPlaceFactory> optional& operator = ( TypedInPlaceFactory const& f ) ;
-
-    T const& get() const ;
-    T&       get() ;
-
-    T const& get_value_or( T const& default ) const ;  [new in 1.34]
-    
-    T const* operator ->() const ;
-    T*       operator ->() ;
-
-    T const& operator *() const ;
-    T&       operator *() ;
-
-    T const* get_ptr() const ;
-    T*       get_ptr() ;
-
-    operator unspecified-bool-type() const ;
-
-    bool operator!() const ;
-
-    deprecated methods
-
-    void reset() ; (deprecated)
-    void reset ( T const& ) ; (deprecated)
-    bool is_initialized() const ; (deprecated)
-
-} ;
-
-template<class T> inline bool operator == ( optional<T> const& x, optional<T> const& y ) ;
-
-template<class T> inline bool operator != ( optional<T> const& x, optional<T> const& y ) ;
-
-template<class T> inline bool operator <  ( optional<T> const& x, optional<T> const& y ) ;
-
-template<class T> inline bool operator >  ( optional<T> const& x, optional<T> const& y ) ;
-
-template<class T> inline bool operator <= ( optional<T> const& x, optional<T> const& y ) ;
-
-template<class T> inline bool operator >= ( optional<T> const& x, optional<T> const& y ) ;
-
-template<class T> inline bool operator == ( optional<T> const& x, T const& n ) ; [new in 1.34]
-
-template<class T> inline bool operator != ( optional<T> const& x, T const& n ) ; [new in 1.34]
-
-template<class T> inline bool operator <  ( optional<T> const& x, T const& n ) ; [new in 1.34]
-
-template<class T> inline bool operator >  ( optional<T> const& x, T const& n ) ; [new in 1.34]
-
-template<class T> inline bool operator <= ( optional<T> const& x, T const& n ) ; [new in 1.34]
-
-template<class T> inline bool operator >= ( optional<T> const& x, T const& n ) ; [new in 1.34]
-
-template<class T> inline bool operator == ( T const& n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator != ( T const& n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator <  ( T const& n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator >  ( T const& n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator <= ( T const& n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator >= ( T const& n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator == ( optional<T> const& x, none_t n ) ; [new in 1.34]
-
-template<class T> inline bool operator != ( optional<T> const& x, none_t n ) ; [new in 1.34]
-
-template<class T> inline bool operator <  ( optional<T> const& x, none_t n ) ; [new in 1.34]
-
-template<class T> inline bool operator >  ( optional<T> const& x, none_t n ) ; [new in 1.34]
-
-template<class T> inline bool operator <= ( optional<T> const& x, none_t n ) ; [new in 1.34]
-
-template<class T> inline bool operator >= ( optional<T> const& x, none_t n ) ; [new in 1.34]
-
-template<class T> inline bool operator == ( none_t n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator != ( none_t n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator <  ( none_t n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator >  ( none_t n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator <= ( none_t n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline bool operator >= ( none_t n, optional<T> const& y ) ; [new in 1.34]
-
-template<class T> inline optional<T> make_optional ( T const& v ) ;  [new in 1.34]
-
-template<class T> inline optional<T> make_optional ( bool condition, T const& v ) ;  [new in 1.34]
-
-template<class T> inline T const& get_optional_value_or ( optional<T> const& opt, T const& default ) ;  [new in 1.34]
-
-template<class T> inline T const& get ( optional<T> const& opt ) ;
-
-template<class T> inline T& get ( optional<T> & opt ) ;
-
-template<class T> inline T const* get ( optional<T> const* opt ) ;
-
-template<class T> inline T* get ( optional<T>* opt ) ;
-
-template<class T> inline T const* get_pointer ( optional<T> const& opt ) ;
-
-template<class T> inline T* get_pointer ( optional<T> & opt ) ;
-
-template<class T> inline void swap( optional<T>& x, optional<T>& y ) ;
-
-} // namespace boost
-
    
-
-
    
-
-
    Detailed Semantics
    
-
-
    NOTES: 
    
-
-
    Because T might be of reference type, in the sequel, those entries whose
-semantic depends on T being of reference type or not will be distinguished using
-the following convention:
    
-If the entry reads: optional<T (not a ref)>, the description corresponds only to
-the case where T is not of reference type.
    
-If the entry reads: optional<T&>, the description corresponds only to the case
-where T is of reference type. 
    
-If the entry reads: optional<T>, the description is the same for both cases.
    
-
-
    The following section contains various assert() which are used only to
-show the postconditions as sample code. It is not implied that the type T must
-support each particular expression but that if the expression is supported, the
-implied condition holds.
    
-
-
    
-
-
    optional<T>::optional();
    
-
    
-
    Effect: Default-Constructs an optional.
    
-
    Postconditions: *this is uninitialized.
    
-
    Throws: Nothing.
    
-
    Notes: T's default constructor is not called.
    
-
    Example:
    
-  
    
-    
    optional<T> def ;
-assert ( !def ) ;
    
-
    
-
    
-
-
    
-
-
    optional<T>::optional( none_t );
    
-
    
-
    Effect: Constructs an optional uninitialized.
    
-
    Postconditions: *this is uninitialized.
    
-
    Throws: Nothing.
    
-
    Notes:
    
-
    
-
    T's default constructor is not called.
    
-The
-expression boost::none denotes an instance of boost::none_t that can be
-used as the parameter.
    
-
    
-
    Example:
    
-  
    
-
    -#include <boost/none.hpp>
-optional<int> n(boost::none) ;
-assert ( !n ) ;
-
    
-
    
-
    
-
-
    
-
-
    optional<T (not a ref)>::optional( T const& v )
    
-
    
-
    Effect: Directly-Constructs an optional.
    
-
    Postconditions: *this is initialized and its value is a copy of 'v'.
    
-
    Throws: Whatever T::T( T const& ) throws.
    
-
    Notes:  T::T( T const& ) is called.
    
-
    Exception Safety: Exceptions can only be thrown during T::T( T const& );
-in that case, this constructor has no effect.
-
    
-
    Example:
    
-
    
-
    -T v;
-optional<T> opt(v);
-assert ( *opt == v ) ;
-
    
-
    
-
    
-
-
    
-
-
    optional<T&>::optional( T& ref )
    
-
    
-
    Effect: Directly-Constructs an optional.
    
-
    Postconditions: *this is initialized and its value is an
-instance of an internal type wrapping the reference 'ref'.
    
-
    Throws: Nothing.
    
-
    Example:
    
-
    
-
    -T v;
-T& vref = v ;
-optional<T&> opt(vref);
-assert ( *opt == v ) ;
-++ v ; // mutate referee
-assert (*opt == v); 
-
    
-
    
-
    
-
-
    
-
-
    optional<T (not a ref)>::optional( bool condition, T const& v ) ;
-optional<T&>           ::optional( bool condition, T&       v ) ;
-
    
-
-
    
-
    If condition is true, same as:
    
-
    optional<T (not a ref)>::optional( T const& v )
-optional<T&>           ::optional( T&       v )
-
    
-
    otherwise, same as:
    
-
    -optional<T (not a ref)>::optional()
-optional<T&>           ::optional()
-
    
-
    
-
-
    
-
-
    optional<T (not a ref)>::optional( optional const& rhs );
    
-
    
-
    Effect: Copy-Constructs an optional.
    
-
    Postconditions: If rhs is initialized, *this is initialized
-and its value is a copy of the value of rhs; else *this
-is uninitialized.
    
-
    Throws: Whatever T::T( T const& ) throws.
    
-
    Notes: If rhs is initialized, T::T(T const& ) is called.
    
-
    Exception Safety: Exceptions can only be thrown during T::T( T const& );
-in that case, this constructor has no effect.
-
    
-
    Example:
    
-
    
-
    -optional<T> uninit ;
-assert (!uninit);
-
-optional<T> uinit2 ( uninit ) ;
-assert ( uninit2 == uninit );
-
-optional<T> init( T(2) );
-assert ( *init == T(2) ) ;
-
-optional<T> init2 ( init ) ;
-assert ( init2 == init ) ;
-
    
-
-
    
-
    
-
-
    
-
-
    optional<T&>::optional( optional const& rhs );
    
-
    
-
    Effect: Copy-Constructs an optional.
    
-
    Postconditions: If rhs is initialized, *this is initialized
-and its value is another reference to the same object referenced by *rhs; else *this
-is uninitialized.
    
-
    Throws: Nothing.
    
-
    Notes: If rhs is initialized, both *this and *rhs will
-reefer to the same object (they alias).
    
-
    Example:
    
-
    
-
    -optional<T&> uninit ;
-assert (!uninit);
-
-optional<T&> uinit2 ( uninit ) ;
-assert ( uninit2 == uninit );
-
-T v = 2 ; T& ref = v ;
-optional<T> init(ref);
-assert ( *init == v ) ;
-
-optional<T> init2 ( init ) ;
-assert ( *init2 == v ) ;
-
-v = 3 ;
-
-assert ( *init  == 3 ) ;
-assert ( *init2 == 3 ) ;
-
-
-
    
-
-
    
-
    
-
-
    
-
-
    template<U> explicit optional<T (not a ref)>::optional( optional<U> const& rhs );
    
-
    
-
    Effect: Copy-Constructs an optional.
    
-
    Postconditions: If rhs is initialized, *this is initialized
-    and its value is a copy of the value of rhs converted
-    to type T; else *this is uninitialized.
-
    
-
    Throws: Whatever T::T( U const& ) throws.
    
-
    Notes: T::T( U const& ) is called if rhs is initialized, which requires
-a valid conversion from U to T.
-
    
-
    Exception Safety: Exceptions can only be thrown during T::T( U const& );
-in that case, this constructor has no effect.
-
    
-
    Example:
    
-
    
-
-
    -optional<double> x(123.4);
-assert ( *x == 123.4 ) ;
-
-optional<int> y(x) ;
-assert( *y == 123 ) ;
-
    
-
    
-
    
-
-
    
-
-
    template<InPlaceFactory> explicit optional<T (not a ref)>::optional( InPlaceFactory const& f );
    
-
-
    template<TypedInPlaceFactory> explicit optional<T (not a ref)>::optional( TypedInPlaceFactory const& f );
    
-
    
-
    Effect: Constructs an optional with a value of T obtained from
-the factory.
    
-
    Postconditions:  *this is initialized and its value is
-directly given from the factory 'f' (i.e., the value is not copied).
    
-
    Throws: Whatever the T constructor called by the factory throws.
    
-
    Notes: See In-Place Factories
    
-
    Exception Safety: Exceptions can only be thrown during the call to the
-T constructor used by the factory;
-in that case, this constructor has no effect.
-
    
-
    Example:
    
-
    
-
-
    -class C { C ( char, double, std::string ) ; } ;
-
-C v('A',123.4,"hello");
-
-optional<C> x( in_place   ('A', 123.4, "hello") ); // InPlaceFactory used
-optional<C> y( in_place<C>('A', 123.4, "hello") ); // TypedInPlaceFactory used
-
-assert ( *x == v ) ;
-assert ( *y == v ) ;
-
-
    
-
    
-
    
-
-
    
-
-
    optional& optional<T>::operator= ( none_t n ) ;
    
-
    
-
    Effect: Same as opeator=(optional const& rhs), when rhs is default-constructed (uninitialized).
    
-
    Postconditions: *this is uninitialized
    
-
    Example:
    
-
    
-
    -#include <boost/none.hpp>
-
-optional<int> def ;
-optional<int> opt(123) ;
-
-opt = boost::none ;
-
-assert ( opt == def ) ;
-
    
-
    
-
    
-
-
    
-
-
    optional& optional<T (not a ref)>::operator= ( T const& rhs ) ;
    
-
    
-
    Effect: Assigns the value 'rhs' to an optional.
    
-
    Postconditions: *this is initialized
-and its value is a copy of rhs.
    
-
    Throws: Whatever T::operator=( T const& ) or T::T(T const&) throws.
    
-
    Notes: If *this was initialized, T's assignment operator is 
-used, otherwise, its copy-constructor is used.
    
-
    Exception Safety: In the event of an exception, the initialization 
-state of *this is unchanged and its value unspecified as far as optional 
-is concerned (it is up to T's operator=()) [If *this is initially 
-uninitialized and T's copy constructor fails, *this is left 
-properly uninitialized]
    
-
    Example:
    
-
    
-
    -T x;
-optional<T> def ;
-optional<T> opt(x) ;
-
-T y;
-def = y ;
-assert ( *def == y ) ;
-opt = y ;
-assert ( *opt == y ) ;
    
-
    
-
    
-
-
    
-
-
    optional<T&>& optional<T&>::operator= ( T& const& rhs ) ;
    
-
    
-
    Effect: (Re)binds thee wrapped reference.
    
-
    Postconditions: *this is initialized
-and it references the same object referenced by rhs.
    
-
    Notes: If *this was initialized, is is rebound to the 
-new object. See here for details on this behavior.
    
-
    Example:
    
-
    
-
    -int a = 1 ;
-int b = 2 ;
-T& ra = a ;
-T& rb = b ;
-optional<int&> def ;
-optional<int&> opt(ra) ;
-
-def = rb ; // binds 'def' to 'b' through 'rb'
-assert ( *def == b ) ;
-*def = a ; // changes the value of 'b' to a copy of the value of 'a'
-assert ( b == a ) ;
-int c = 3;
-int& rc = c ;
-opt = rc ; // REBINDS to 'c' through 'rc'
-c = 4 ;
-assert ( *opt == 4 ) ;
-
    
-
    
-
    
-
-
    
-
-
    optional& optional<T (not a ref)>::operator= ( optional const& rhs ) ;
    
-
    
-
    Effect: Assigns another optional to an optional.
    
-
    Postconditions: If rhs is initialized, *this is initialized
-and its value is a copy of the value of rhs; else *this
-is uninitialized.
-
    
-
    Throws: Whatever T::operator( T const&) or  T::T( T const& ) throws.
    
-
    Notes: If both *this and rhs are initially initialized, 
-T's assignment operator is used. If *this is initially initialized but 
-rhs is uninitialized, T's destructor is called. If *this is initially 
-uninitialized but rhs is initialized, T's copy constructor is called.
-
    
-
    Exception Safety: In the event of an exception, the initialization 
-state of *this is unchanged and its value unspecified as far as optional 
-is concerned (it is up to T's operator=()) [If *this is initially 
-uninitialized and T's copy constructor fails, *this is left 
-properly uninitialized]
    
-
    Example:
    
-
    
-    
    T v;
-optional<T> opt(v);
-optional<T> def ;
-
-opt = def ;
-assert ( !def ) ;
-// previous value (copy of 'v') destroyed from within 'opt'.
-
-
    
-
    
-
    
-
-
    
-
-
    optional<T&> & optional<T&>::operator= ( optional<T&> const& rhs ) ;
    
-
    
-
    Effect: (Re)binds thee wrapped reference.
    
-
    Postconditions: If *rhs is initialized, *this is initialized
-and it references the same object referenced by *rhs; otherwise, *this 
-is uninitialized (and references no object).
    
-
    Notes: If *this was initialized and so is *rhs, this 
-is is rebound to the new object. See here for details on this 
-behavior.
    
-
    Example:
    
-
    
-    
    int a = 1 ;
-int b = 2 ;
-T& ra = a ;
-T& rb = b ;
-optional<int&> def ;
-optional<int&> ora(ra) ;
-optional<int&> orb(rb) ;
-
-def = orb ; // binds 'def' to 'b' through 'rb' wrapped within 'orb'
-assert ( *def == b ) ;
-*def = ora ; // changes the value of 'b' to a copy of the value of 'a'
-assert ( b == a ) ;
-int c = 3;
-int& rc = c ;
-optional<int&> orc(rc) ;
-ora = orc ; // REBINDS ora to 'c' through 'rc'
-c = 4 ;
-assert ( *ora == 4 ) ;
-
    
-
    
-
    
-
-
    
-
-
    template<U> optional& optional<T (not a ref)>::operator= ( optional<U> const& rhs ) ;
    
-
    
-
    Effect: Assigns another convertible optional to an optional.
    
-
    Postconditions: If rhs is initialized, *this is initialized
-and its value is a copy of the value of rhs converted
-to type T; else *this is uninitialized.
-
    
-
    Throws: Whatever T::operator=( U const& ) or T::T( U const& ) throws.
    
-
    Notes: If both *this and rhs are initially initialized, 
-T's assignment operator (from U) is used. If *this is initially initialized but 
-rhs is uninitialized, T's destructor is called. If *this is initially 
-uninitialized but rhs is initialized, T's converting constructor (from U) is called.
-
    
-
    Exception Safety: In the event of an exception, the initialization 
-state of *this is unchanged and its value unspecified as far as optional 
-is concerned (it is up to T's operator=()) [If *this is initially 
-uninitialized and T's converting constructor fails, *this is left 
-properly uninitialized]
    
-
    Example:
    
-
    
-    
    T v;
-optional<T> opt0(v);
-optional<U> opt1;
-
-opt1 = opt0 ;
-assert ( *opt1 == static_cast<U>(v) ) ;
-
    
-
    
-
    
-
-
    
-
    void optional<T (not a ref)>::reset( T const& v ) ;
    
-
    
-
    Deprecated: same as operator= ( T const& v) ;
    
-
    
-
-
    
-
    void optional<T>::reset() ;
    
-
    
-
    Deprecated: Same as operator=( none_t n);
    
-
    
-
-
    
-
-
    T const& optional<T (not a ref)>::operator*() const ;
-T&       optional<T (not a ref)>::operator*();
    
-
-
    T const& optional<T (not a ref)>::get() const ;
-T&       optional<T (not a ref)>::get() ;
-
-inline T const& get ( optional<T (not a ref)> const& ) ;
-inline T&       get ( optional<T (not a ref)> &) ;
-
    
-
    
-
    Requirements: *this is initialized
    
-
    Returns: A reference to the contained value
    
-
    Throws: Nothing.
    
-
    Notes: The requirement is asserted via BOOST_ASSERT().
    
-
    Example:
    
-
    
-    
    T v ;
-optional<T> opt ( v );
-T const& u = *opt;
-assert ( u == v ) ;
-T w ;
-*opt = w ;
-assert ( *opt == w ) ;
-
    
-  
    
-    
    
-
    
-
-
    
-
-
-
    T const& optional<T&>::operator*() const ;
-T      & optional<T&>::operator*();
    
-
-
    T const& optional<T&>::get() const ;
-T&       optional<T&>::get() ;
-
-inline T const& get ( optional<T&> const& ) ;
-inline T&       get ( optional<T&> &) ;
-
    
-
    
-
    Requirements: *this is initialized
    
-
    Returns: The reference contained.
    
-
    Throws: Nothing.
    
-
    Notes: The requirement is asserted via BOOST_ASSERT().
    
-
    Example:
    
-
    
-    
    T v ;
-T& vref = v ;
-optional<T&> opt ( vref );
-T const& vref2 = *opt;
-assert ( vref2 == v ) ;
-++ v ;
-assert ( *opt == v ) ;
    
-  
    
-
    
-
-
    
-
-
    T const& optional<T>::get_value_or( T const& default) const ;
-T&       optional<T>::get_value_or( T&       default ) ;
-
-inline T const& get_optional_value_or ( optional<T> const& o, T const& default ) ;
-inline T&       get_optional_value_or ( optional<T>&       o, T&       default ) ;
-
    
-
    
-
    Returns: A reference to the contained value (which can be itself a reference), if any, or default
    
-
    Throws: Nothing.
    
-
    Example:
    
-
    
-    
    T v, z ;
-optional<T> def;
-T const& y = def.get_value_or(z);
-assert ( y == z ) ;
-
-optional<T> opt ( v );
-T const& u = get_optional_value_or(opt,z);
-assert ( u == v ) ;
-assert ( u != z ) ;
-
    
-  
    
-    
    
-
    
-
-
    
-
-
    T const* optional<T>::get_ptr() const ;
-T*       optional<T>::get_ptr() ;
-
-inline T const* get_pointer ( optional<T> const& ) ;
-inline T*       get_pointer ( optional<T> &) ;
-
    
-
    
-
    Returns: If *this is initialized, a pointer to the contained
-value; else 0 (null).
-
    
-
    Throws: Nothing.
    
-
    Notes: If T is a reference type, the pointer is to the referenced object
    
-
    Notes: The contained value is permanently stored within *this, so
-you should not hold nor delete this pointer.
-
    
-
    Example:
    
-
    
-    
    int v=123;
-optional<int> opt(v);
-optional<int> const copt(v);
-int* p = opt.get_ptr() ;
-int const* cp = copt.get_ptr();
-assert ( p == get_pointer(opt) );
-assert ( cp == get_pointer(copt) ) ;
-
-int& rv = v ;
-optional<int&> optr(rv);
-
-*(optr.get_ptr()) = 456 ;
-
-assert ( v == 456 );
-
-
-
    
-
    
-
    
-
-
-
    
-
-
-
    T const* optional<T>::operator ->() const ;
-T*       optional<T>::operator ->()       ;
-
    
-
    
-
    Requirements: *this is initialized.
    
-
    Returns: A pointer to the contained value.
    
-
    Throws: Nothing.
    
-
    Notes: If T is a reference type, the pointer is to the referenced object
    
-
    Notes: The requirement is asserted via BOOST_ASSERT().
    
-
    Example:
    
-
    
-
    struct X { int mdata ; } ;
-X x ;
-optional<X> opt (x);
-opt->mdata = 2 ;
-
-X& rx = x ;
-
-optional<X&> optr (rx);
-optr->mdata = 4 ;
-
-assert ( x.mdata = 4 ) 
-
-
    
-
    
-
    
-
-
-
    
-
-
-
    optional<T>::operator unspecified-bool-type() const ;
    
-
    
-
    Returns: An unspecified value which if used on a boolean context is equivalent to (get() != 0)
    
-
    Throws: Nothing.
    
-
    
-    
    optional<T> def ;
-assert ( def == 0 );
-optional<T> opt ( v ) ;
-assert ( opt );
-assert ( opt != 0 );
-
    
-
    
-
    
-
-
    
-
-
-
     bool optional<T>::operator!() ;
    
-
    
-
    Returns: If *this is uninitialized, true; else false.
    
-
    Throws: Nothing.
    
-
    Notes: This operator is provided for those compilers which can't use
-the unspecified-bool-type operator in certain boolean contexts.
-
    
-
    Example:
    
-
    
-    
    optional<T> opt ;
-assert ( !opt );
-*opt = some_T ;
-
-// Notice the "double-bang" idiom here.
-assert ( !!opt ) ;
-
    
-
    
-
    
-
-
-
    
-
-
-
    bool optional<T>::is_initialized() const ;
    
-
    
-
    Returns: true is the optional is initialized, false
-otherwise.
    
-
    Throws: Nothing.
    
-
    
-    
    optional<T> def ;
-assert ( !def.is_initialized() );
-optional<T> opt ( v ) ;
-assert ( opt.is_initialized() );
    
-
    
-
    
-
-
    
-
-
    optional<T (not a ref)> make_optional( T const& v )
    
-
    
-
    Returns: optional<T>(v) for the deduced type T of v.
    
-
    Example:
    
-
    
-
    template<class T> void foo ( optional<T> const& opt ) ;
-
-foo ( make_optional(1+1) ) ; // Creates an optional<int>
-
    
-
    
-
    
-
-
    optional<T (not a ref)> make_optional( bool condition, T const& v )
    
-
    
-
    Returns: optional<T>(condition,v) for the deduced type T of v.
    
-
    Example:
    
-
    
-
    optional<double> calculate_foo()
-{
-  double val = compute_foo();
-  return make_optional(is_not_nan_and_finite(val),val);
-}
-
-optional<double> v = calculate_foo();
-if ( !v )
-  error("foo wasn't computed");
-
    
-
    
-
-
    
-
-
-
    bool operator == ( optional<T> const& x, optional<T> const& y );
    
-
    
-
    Returns: If both x and y are initialied, (*x == *y).
-If only x or y is initialized, false. If both are uninitialized, true. 
    
-
    Throws: Nothing.
    
-
    Notes: Pointers have shallow relational operators while optional has
-deep relational operators. Do not use operator == directly in generic code
-which expect to be given either an optional<T> or a pointer;
-use equal_pointees() instead 
    
-
    Example:
    
-
    
-    
    T x(12);
-T y(12);
-T z(21);
-optional<T> def0 ;
-optional<T> def1 ;
-optional<T> optX(x);
-optional<T> optY(y);
-optional<T> optZ(z);
-
-// Identity always hold
-assert ( def0 == def0 );
-assert ( optX == optX );
-
-// Both uninitialized compare equal
-assert ( def0 == def1 );
-
-// Only one initialized compare unequal.
-assert ( def0 != optX );
-
-// Both initialized compare as (*lhs == *rhs)
-assert ( optX == optY ) ;
-assert ( optX != optZ ) ;
-
    
-
    
-
    
-
-
    
-
-
-
    bool operator < ( optional<T> const& x, optional<T> const& y );
    
-
    
-
    Returns: If y is not initialized, false.
-If y is initialized and x is not initialized, true.
-If both x and y are initialized, (*x < *y). 
    
-
    Throws: Nothing.
    
-
    Notes: Pointers have shallow relational operators while optional has
-deep relational operators. Do not use operator < directly in generic code
-which expect to be given either an optional<T> or a pointer;
-use less_pointees() instead 
    
-
    Example:
    
-
    
-    
    T x(12);
-T y(34);
-optional<T> def ;
-optional<T> optX(x);
-optional<T> optY(y);
-
-// Identity always hold
-assert ( !(def < def) );
-assert ( optX == optX );
-
-// Both uninitialized compare equal
-assert ( def0 == def1 );
-
-// Only one initialized compare unequal.
-assert ( def0 != optX );
-
-// Both initialized compare as (*lhs == *rhs)
-assert ( optX == optY ) ;
-assert ( optX != optZ ) ;
-
    
-
    
-
    
-
-
    
-
    bool operator != ( optional<T> const& x, optional<T> const& y );
-
    
-
    
-  
    Returns: !( x == y );
    
-  
    Throws: Nothing.
    
-
    
-
-
    
-
    bool operator > ( optional<T> const& x, optional<T> const& y );
-
    
-
    
-  
    Returns: ( y < x );
    
-  
    Throws: Nothing.
    
-
    
-
-
    
-
    bool operator <= ( optional<T> const& x, optional<T> const& y );
-
    
-
    
-  
    Returns: !( y<x );
    
-  
    Throws: Nothing.
    
-
    
-
-
    
-
    bool operator >= ( optional<T> const& x, optional<T> const& y );
-
    
-
    
-  
    Returns: !( x<y );
    
-  
    Throws: Nothing.
    
-
    
-
-
    
-
    -bool operator == ( optional<T> const& x, T const& n );
-bool operator != ( optional<T> const& x, T const& n );
-bool operator <  ( optional<T> const& x, T const& n );
-bool operator >  ( optional<T> const& x, T const& n );
-bool operator <= ( optional<T> const& x, T const& n );
-bool operator >= ( optional<T> const& x, T const& n );
-bool operator == ( T const& n, optional<T> const& y );
-bool operator != ( T const& n, optional<T> const& y );
-bool operator <  ( T const& n, optional<T> const& y );
-bool operator >  ( T const& n, optional<T> const& y );
-bool operator <= ( T const& n, optional<T> const& y );
-bool operator >= ( T const& n, optional<T> const& y );
-
    
-
    
-  
    Returns: The result obtained by replacing the argument 'n' by optional<T>(n).
    
-
    
-
-
    
-
    -bool operator == ( optional<T> const& x, none_t n );
-bool operator != ( optional<T> const& x, none_t n );
-bool operator <  ( optional<T> const& x, none_t n );
-bool operator >  ( optional<T> const& x, none_t n );
-bool operator <= ( optional<T> const& x, none_t n );
-bool operator >= ( optional<T> const& x, none_t n );
-bool operator == ( none_t n, optional<T> const& y );
-bool operator != ( none_t n, optional<T> const& y );
-bool operator <  ( none_t n, optional<T> const& y );
-bool operator >  ( none_t n, optional<T> const& y );
-bool operator <= ( none_t n, optional<T> const& y );
-bool operator >= ( none_t n, optional<T> const& y );
-
    
-
    
-  
    Returns: The result obtained by replacing the argument 'n' by optional<T>().
    
-
    
-
    
-
-
    void swap ( optional<T>& x, optional<T>& y );
    
-
-
    
-
    Effect: If both x and y are initialized, calls swap(*x,*y) using std::swap.
    
-If only one is initialized, say x, calls: y = *x; x = boost:none;
    
-If none is initialized, does nothing. 
    
-
    Postconditions: The states of x and y interchanged.
    
-
    Throws: If both are initialized, whatever swap(T&,T&) throws.
-If only one is initialized, whatever T::T ( T const& ) throws. 
    
-
    Notes: If both are initialized, swap(T&,T&) is used unqualified but with std::swap introduced in scope.
    
-If only one is initialized, T::~T() and T::T( T const& ) is called. 
    
-
    Exception Safety: If both are initialized, this operation has the exception
-safety guarantees of swap(T&,T&).
    
-If only one is initialized, it has the same basic guarantee as optional<T>::operator=( T const& ). 
    
-
    Example:
    
-
    
-      
    T x(12);
-T y(21);
-optional<T> def0 ;
-optional<T> def1 ;
-optional<T> optX(x);
-optional<T> optY(y);
-
-boost::swap(def0,def1); // no-op
-
-boost::swap(def0,optX);
-assert ( *def0 == x );
-assert ( !optX );
-
-boost::swap(def0,optX); // Get back to original values
-
-boost::swap(optX,optY);
-assert ( *optX == y );
-assert ( *optY == x );
-
-
    
-
    
-
    
-
    
-
-
    Examples
    
-
-
    Optional return values
    
-
    optional<char> get_async_input()
-{
-  if ( !queue.empty() )
-       return optional<char>(queue.top());
-  else return optional<char>(); // uninitialized
-}
-
-void receive_async_message()
-{
-  optional<char> rcv ;
-  // The safe boolean conversion from 'rcv' is used here.
-  while ( (rcv = get_async_input()) && !timeout() )
-    output(*rcv);
-}
-
    
-
-
    Optional local variables
    
-
    optional<string> name ;
-if ( database.open() )
-{
-  name = database.lookup(employer_name) ;
-}
-else
-{
-  if ( can_ask_user )
-    name = user.ask(employer_name) ;
-}
-
-if ( name )
-     print(*name);
-else print("employer's name not found!");
-
    
-
-
    Optional data members
    
-
    class figure
-{
-  public:
-
-    figure()
-    {
-      // data member 'm_clipping_rect' is uninitialized at this point.
-    }
-
-    void clip_in_rect ( rect const& rect )
-      {
-         ....
-         m_clipping_rect = rect ; // initialized here.
-      }
-
-    void draw ( canvas& cvs )
-      {
-        if ( m_clipping_rect )
-          do_clipping(*m_clipping_rect);
-
-        cvs.drawXXX(..);
-      }
-
-    // this can return NULL.
-    rect const* get_clipping_rect() { return get_pointer(m_clipping_rect); }
-
-  private :
-
-    optional<rect> m_clipping_rect ;
-
-};
-
    
-
    Bypassing expensive unnecessary default construction
    
-
    class ExpensiveCtor { ... } ;
-class Fred
-{
-  Fred() : mLargeVector(10000) {}
-
-  std::vector< optional<ExpensiveCtor> > mLargeVector ;
-} ;
-
    
-
-
    
-
-
    Optional references
    
-
    This library allows the template parameter T to be of reference type: T&, and
-to some extent, T const&.
    
-
-
    However, since references are not real objects some restrictions apply and
-some operations are not available in this case:
    
-
-
      
-  
    • Converting constructors
      • 
-  
    • Converting assignment
      • 
-  
    • InPlace construction
      • 
-  
    • InPlace assignment
      • 
-
    
-
    Also, even though optional<T&> treats it wrapped pseudo-object much as a real
-value, a true real reference is stored, thus aliasing can ocurr: 
    
-
-
      
-  
    • Copies of optional<T&> copies the reference, but all copied references
-  will nonetheless reefer to the same object.
      • 
-  
    • Value-access provides access to the referenced object rather
-  than the reference itself.
      • 
-  
    • Pointer-access provides a pointer to the referenced object rather
-  than a pointer to the reference itself.
      • 
-
    
-
-
    
-
    Rebinding semantics for assignment of optional 
-references
    
-
    If you assign to an uninitialized optional<T&> the effect is to bind (for the first time) to the object. 
-Clearly, there is no other choice.
    
-
    int x = 1 ;
-int& rx = x ;
-optional<int&> ora ;
-optional<int&> orb(rx) ;
-ora = orb ; // now 'ora' is bound to 'x' through 'rx'
-*ora = 2 ; // Changes value of 'x' through 'ora'
-assert(x==2); 
-
    
-
    If you assign to a bare C++ reference, the assignment is forwarded to the 
-referenced object; it's value changes but the reference is never rebound.
    
-
    int a = 1 ;
-int& ra = a ;
-int b = 2 ;
-int& rb = b ;
-ra = rb ; // Changes the VALUE of 'a' to that of 'b'
-assert(a==b);
-b = 3 ;
-assert(ra!=b); // 'ra' is not rebound to 'b'
-
    
-
    Now, if you assign to an initialized optional<T&>, the effect is to rebind to the new object instead of assigning the referee. This is unlike 
-bare C++ references.
    
-
    int a = 1 ;
-int b = 2 ;
-int& ra = a ;
-int& rb = b ;
-optional<int&> ora(ra) ;
-optional<int&> orb(rb) ;
-ora = orb ; // 'ora' is rebound to 'b'
-*ora = 3 ; // Changes value of 'b' (not 'a')
-assert(a==1); 
-assert(b==3); 
-
    
-
    Rationale:
    
-
    Rebinding semantics for the assignment of initialized optional 
-references has been chosen to provide consistency among initialization 
-states even at the expense of lack of consistency with the semantics of bare 
-C++ references.
    
-It is true that optional<U> strives to behave as much as possible as U does 
-whenever it is initialized; but in the case when U is T&, doing so would result 
-in inconsistent behavior w.r.t to the lvalue initialization state.
    
-
    Consider the following code :
    
-
    -int x = 1 ;
-int& rx = x ;
-void foo ( optional<int&> & outer )
-{
-  optional<int&> b(rx);
-  outer = b ;
-}
-
    
-
    What should the assignment to 'outer' do?
    
-If 'outer' is uninitialized, the answer is clear: it should bind to 'x' (so we now have 
-a second reference to 'x').
    
-But what if 'outer' is already initialized?
    
-The assignment could change the value of the 
-referenced object (whatever that is), but doing that would be inconsistent with the uninitialized case
-and then you wouldn't be able to reason at compile time about all the references to x since
-the appearance of a new reference to it would depend on wheter the lvalue ('outer')
-is initialized or not.
    
-
    Arguably, if rebinding the reference to another object is wrong for your code, then is 
-likely that binding it for the fist time via assignment instead of intialization is also wrong.
-In that case, you can always just assign the value to the referenced object directly via
-the access operator *opt=value.
    
-
    If rebinding is wrong but first-time binding 
-isn't (via assignment), you can always work around the rebinding semantics using a discriminator:
    
-
    -if ( !opt )
-      opt = value ; // first-time binding
-else *opt = value ; // assign to referee without rebinding 
-
    
-
-
    
-
-
    none_t and none
    
-
    optional<T> supports uninitialized states with a convenient syntax via a constant of 
-the implementation-defined type boost::none_t, identified as boost::none.
    
-
    Starting with Boost version 1.34.0, both boost::none_t and boost::none are
-included in boost/none.hpp, which is automatically included by boost/optional/optional.hpp
-
    
-
    This contant is similar in purpose to NULL, except that is not a null pointer value. You can use it to initialize  
-an optional<T> instance, which has the same effect of a default constructor, and you can assign it which has the 
-effect of reseting the optional<T> instance. You can also use it in relational operators to make the predicate expression
-more clear.
    
-
    Here are some typical examples:
    
-
    -#include "boost/optional/optional.hpp" // boost/none.hpp is included automatically
-
-boost::optional<int> foo ( int a )
-{
-  return some_condition(a) ? boost::make_optional(a) : boost::none ;  
-  
-  // NOTE: in real code you can just use this: make_optional(some_condition(a), a ) 
-}
-
-boost::optional<int> opt = boost::none ;
-
-if ( opt == boost::none )
-  opt = foo(123);
-
-opt = boost::none ;
-
-
    
-
-
    
-
-
    In-Place Factories
    
-
    
-One of the typical problems with wrappers and containers is that their
-interfaces usually provide an operation to initialize or assign the contained
-object as a copy of some other object. This not only requires the underlying
-type to be Copy Constructible, but also requires the existence of a fully
-constructed object, often temporary, just to follow the copy from:
    
-
    struct X
-{
-  X ( int, std:::string ) ;
-} ;
    
-
    class W
-{
-  X wrapped_ ;
-
-public:
-
-  W ( X const& x ) : wrapped_(x) {}
-} ;
    
-
    void foo()
-{
-  // Temporary object created.
-  W ( X(123,"hello") ) ;
-}
-
    
-
    A solution to this problem is to support direct construction of the contained
-object right in the container's storage.
    
-In this scheme, the user only needs to supply the arguments to the constructor
-to use in the wrapped object construction.
    
-
    class W
-{
-  X wrapped_ ;
-
-public:
-
-  W ( X const& x ) : wrapped_(x) {}
-  W ( int a0, std::string a1) : wrapped_(a0,a1) {}
-} ;
    
-
    void foo()
-{
-  // Wrapped object constructed in-place
-  // No temporary created.
-  W (123,"hello") ;
-}
-
    
-
    A limitation of this method is that it doesn't scale well to wrapped objects with multiple
-constructors nor to generic code were the constructor overloads are unknown.
    
-
    The solution presented in this library is the family of InPlaceFactories and TypedInPlaceFactories.
    
-These factories are a family of classes which encapsulate an increasing number of arbitrary
-constructor parameters and supply a method to construct an object of a given type using those
-parameters at an address specified by the user via placement new.
    
-
     For example, one member of this family looks like:
    
-
    template<class T,class A0, class A1>
-class TypedInPlaceFactory2
-{
-  A0 m_a0 ; A1 m_a1 ;
-
-public:
-
-  TypedInPlaceFactory2( A0 const& a0, A1 const& a1 ) : m_a0(a0), m_a1(a1) {}
-
-  void construct ( void* p ) { new (p) T(m_a0,m_a1) ; }
-} ;
-
    
-
    A wrapper class aware of this can use it as:
    
-
    class W
-{
-  X wrapped_ ;
-
-public:
-
-  W ( X const& x ) : wrapped_(x) {}
-  W ( TypedInPlaceFactory2 const& fac ) { fac.construct(&wrapped_) ; }
-} ;
    
-
    void foo()
-{
-  // Wrapped object constructed in-place via a TypedInPlaceFactory.
-  // No temporary created.
-  W ( TypedInPlaceFactory2<X,int,std::string&rt;(123,"hello")) ;
-}
-
    
-
    The factories are divided in two groups:
      
-  
    • TypedInPlaceFactories: those which take the target type as a primary template parameter.
      • 
-  
    • InPlaceFactories: those with a template construct(void*) member function taking the target type.
      • 
-  
    
-
    Within each group, all the family members differ only in the number of parameters allowed.
    
-
    
-
    This library provides an overloaded set of helper template functions to construct these factories
-without requiring unnecessary template parameters:
    
-
    template<class A0,...,class AN>
-InPlaceFactoryN <A0,...,AN> in_place ( A0 const& a0, ..., AN const& aN) ;
-
-template<class T,class A0,...,class AN>
-TypedInPlaceFactoryN <T,A0,...,AN> in_place ( T const& a0, A0 const& a0, ..., AN const& aN) ;
    
-
-
    In-place factories can be used generically by the wrapper and user as follows:
    
-
    class W
-{
-  X wrapped_ ;
-
-public:
-
-  W ( X const& x ) : wrapped_(x) {}
-
-  template
-  W ( InPlaceFactory const& fac ) { fac.template <X>construct(&wrapped_) ; }
-
-} ;
    
-
    void foo()
-{
-  // Wrapped object constructed in-place via a InPlaceFactory.
-  // No temporary created.
-  W ( in_place(123,"hello") ) ;
-}
-
    
-
    The factories are implemented in the headers: in_place_factory.hpp and typed_in_place_factory.hpp 
    
-
-
    
-
-
    A note about optional<bool>
    
-
    optional<bool> should be used with special caution and consideration.
    
-
    First, it is functionally similar to a tristate boolean (false,maybe,true) —such as boost::tribool—except that in a tristate boolean,
-the maybe state represents a valid value, unlike the corresponding state
-of an uninitialized optional<bool>.
    
-It should be carefully considered if an optional<bool> instead of a tribool is really needed
    
-
    Second, optional<> provides a simple way to test initialization state: an implicit conversion to a type that evaluates as a 'bool' in a boolean context.
    
-Using optional<bool> can lead to subtle errors due to this implicit conversion:
    
-
    void foo ( bool v ) ;
-void bar()
-{
-  optional<bool> v = try();
-
-  // The following intended to pass the value of 'v' to foo():
-  foo(v);
-  // But instead, the initialization state is passed
-  // due to a typo: it should have been foo(*v).
-}
-
    
-
    The only implicit conversion is to bool, and it is safe in the sense that typical
-integral promotions don't apply (i.e. if foo() takes an 'int' instead, it won't compile). 
    
-
-
    Exception Safety Guarantees
    
-
-
    Assignment:
    
-
    IMPORTANT NOTE: This changed in 1.33.1 with respect to previous versions
    
-
    Because of the current implementation (see Implementation Notes), all
-of the assignment methods:
    
-
      
-  
    •  optional<T>::operator= ( optional<T> const& ) 
-  
      • 
-  
    •  optional<T>::operator= ( T const& ) 
      • 
-  
    •  template<class U> optional<T>::operator= ( optional<U> const& ) 
-  
      • 
-  
    •  template<class InPlaceFactory> optional<T>::operator= (
-  InPlaceFactory const& ) 
      • 
-  
    •  template<class TypedInPlaceFactory> optional<T>::operator= (
-  TypedInPlaceFactory const& ) 
      • 
-
    
-
    cannot offer any exception safety guarantee beyond that provided by T::operator=( T const& )
    
-
    On the other hand, the uninitializing methods:
    
-
      
-  
    • optional<T>::operator= ( detail::none_t ) 
      • 
-
    
-
    Provides the no-throw guarantee (assuming a no-throw T::~T()) becuse it only destroys the stored object.
    
-
-
    Swap:
    
-
    void swap( optional<T>&, optional<T>& ) has the same exception guarantee as swap(T&,T&) when both optionals are initialized.
    
-If only one of the optionals is initialized, it gives the same exception guarantee as T::operator=( T const& ) (since optional<T>::operator=( none_t ) doesn't throw).
    
-If none of the optionals is initialized, it has no-throw guarantee since it is a no-op. 
    
-
-
    
-
-
    Type requirements
    
-
    In general, T must be Copy Constructible and have a no-throw destructor. The copy-constructible requirement is not needed
-if InPlaceFactories are used.
    
-T is not required to be Default Constructible 
    
-
-
    
-
-
    Implementation Notes
    
-
    optional<T> is currently implemented
-  using a custom aligned storage facility built from alignment_of and type_with_alignment (both from Type Traits). 
-  It uses a separate boolean flag to indicate the initialization state.
    
-
    Placement new with T's copy constructor and T's destructor
-  is explicitly used to initialize and destroy optional values. This allows T's default constructor to be effectively by-passed.
    
-
    If assignment is used and the lvalue optional is uninitialized, T's copy constructor is used. However, if it is already initialized, T's assignment operator is used. This prevents optional from offering any exception guarantee stronger than the one offered by the type T itself
    
-
-
    
-
-
    Dependencies and Portability
    
-
-
    The implementation uses type_traits/alignment_of.hpp and type_traits/type_with_alignment.hpp
    
-
-
    
-
-
    Acknowledgments
    
-
    Pre-formal review:
    
-
    
-
    Peter Dimov suggested the name 'optional', and was the first to point out the
-  need for aligned storage
    
-  Douglas Gregor developed 'type_with_alignment', and later Eric Friedman coded
-  'aligned_storage', which are the core of the optional class implementation.
    
-  Andrei Alexandrescu and Brian Parker also worked with aligned storage techniques
-  and their work influenced the current implementation.
    
-  Gennadiy Rozental made extensive and important comments which shaped the design.
    
-  Vesa Karvonen and Douglas Gregor made quite useful comparisons between optional,
-  variant and any; and made other relevant comments. Douglas Gregor and Peter
-  Dimov commented on comparisons and evaluation in boolean contexts.
    
-  Eric Friedman helped understand the issues involved with aligned storage, move/copy
-  operations and exception safety.
    
-  Many others have participated with useful comments: Aleksey Gurotov, Kevlin
-  Henney, David Abrahams, and others I can't recall. 
    
-
    
-
    Post-formal review:
    
-
    
-  
    William Kempf carefully considered the originally proposed interface and
-    suggested the new interface which is currently used. He also started and fueled
-    the discussion about the analogy optional<>/smart pointer and about
-    relational operators.
    
-    Peter Dimov, Joel de Guzman, David Abrahams, Tanton Gibbs and Ian Hanson focused
-    on the relational semantics of optional (originally undefined); concluding
-    with the fact that the pointer-like interface doesn't make it a pointer so
-    it shall have deep relational operators.
    
-    Augustus Saunders also explored the different relational semantics between
-    optional<> and a pointer and developed the OptionalPointee concept as
-    an aid against potential conflicts on generic code.
    
-    Joel de Guzman noticed that optional<> can be seen as an API on top
-    of variant<T,nil_t>.
    
-    Dave Gomboc explained the meaning and usage of the Haskell analog to optional<>:
-    the Maybe type constructor (analogy originally pointed out by David Sankel).
    
-    Other comments were posted by Vincent Finn, Anthony Williams, Ed Brey, Rob
-    Stewart, and others.
    
-    Joel de Guzman made the case for the support of references and helped with
-    the proper semantics.
    
-    Mat Marcus shown the virtues of a value-oriented interface, influencing the
-    current design, and contributed the idea of "none".
    
-
    
-
    
-
-
    Revised March 27, 2007
    
-
    © Copyright Fernando Luis Cacciola Carballal, 2003-2007
    
-
     Use, modification, and distribution are subject to the Boost Software
-License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)
    
-
    Developed by Fernando Cacciola,
-the latest version of this file can be found at www.boost.org, and the boost discussion lists
    
-
    
-
\ No newline at end of file
diff --git a/doc/optional.qbk b/doc/optional.qbk
index 388f686..7388b5f 100644
--- a/doc/optional.qbk
+++ b/doc/optional.qbk
@@ -40,11 +40,6 @@ Distributed under the Boost Software License, Version 1.0.
 
 [/ Icons ]
 
-[def __NOTE__ [$images/note.png]]
-[def __ALERT__ [$images/caution.png]]
-[def __DETAIL__ [$images/note.png]]
-[def __TIP__ [$images/tip.png]]
-[def __QUESTION_MARK__ [$images/question.png]]
 [def __SPACE__ [$images/space.png]]
 [def __GO_TO__ [$images/callouts/R.png]]
 
diff --git a/doc/reference.qbk b/doc/reference.qbk
index 73993b3..c50b61a 100644
--- a/doc/reference.qbk
+++ b/doc/reference.qbk
@@ -126,6 +126,7 @@
 Because `T` might be of reference type, in the sequel, those entries whose
 semantic depends on `T` being of reference type or not will be distinguished
 using the following convention:
+
 * If the entry reads: `optional`, the description
 corresponds only to the case where `T` is not of reference type.
 * If the entry reads: `optional`, the description corresponds only to

From 472a68c92012d523f9df93f76f233a5e781cb490 Mon Sep 17 00:00:00 2001
From: Matias Capeletto 
Date: Thu, 14 Feb 2008 17:44:21 +0000
Subject: [PATCH 10/18] redirect optional docs to new version

[SVN r43248]
---
 index.html | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/index.html b/index.html
index ed59314..3031e05 100644
--- a/index.html
+++ b/index.html
@@ -1,11 +1,11 @@
 
 
-
+
 
 
 Automatic redirection failed, please go to
-doc/optional.html. 
    
-
    © Copyright Beman Dawes, 2001
    
+doc/html/index.html. 
    
+
    � Copyright Beman Dawes, 2001
    
 
    Distributed under the Boost Software License, Version 1.0. (See accompanying 
 file LICENSE_1_0.txt or copy 
 at www.boost.org/LICENSE_1_0.txt)
    

From 66c366d18a416fd1f3500581ef44a0f9d584a74b Mon Sep 17 00:00:00 2001
From: Niels Dekker 
Date: Fri, 25 Apr 2008 16:50:32 +0000
Subject: [PATCH 11/18] Improved swap for optional, co-written by Thorsten
 and Fernando: added support for tweaking whether swap should use T's default
 constructor. Added swap member function. Discussed at Boost developers'
 mailing list, "[optional] problems with swap()",
 http://lists.boost.org/Archives/boost/2008/04/135882.php

[SVN r44766]
---
 include/boost/optional/optional.hpp | 104 ++++++++++++++++++++--------
 1 file changed, 75 insertions(+), 29 deletions(-)

diff --git a/include/boost/optional/optional.hpp b/include/boost/optional/optional.hpp
index ebcf17a..f23df09 100644
--- a/include/boost/optional/optional.hpp
+++ b/include/boost/optional/optional.hpp
@@ -1,4 +1,4 @@
-// Copyright (C) 2003, Fernando Luis Cacciola Carballal.
+// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
 //
 // Use, modification, and distribution is subject to the Boost Software
 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
@@ -9,6 +9,9 @@
 // You are welcome to contact the author at:
 //  fernando_cacciola@hotmail.com
 //
+// Revisions:
+// 25 Apr 2008 (improved swap) Fernando Cacciola, Niels Dekker, Thorsten Ottosen
+// 
 #ifndef BOOST_OPTIONAL_OPTIONAL_FLC_19NOV2002_HPP
 #define BOOST_OPTIONAL_OPTIONAL_FLC_19NOV2002_HPP
 
@@ -19,6 +22,7 @@
 #include "boost/assert.hpp"
 #include "boost/type.hpp"
 #include "boost/type_traits/alignment_of.hpp"
+#include "boost/type_traits/has_nothrow_constructor.hpp"
 #include "boost/type_traits/type_with_alignment.hpp"
 #include "boost/type_traits/remove_reference.hpp"
 #include "boost/type_traits/is_reference.hpp"
@@ -28,6 +32,7 @@
 #include "boost/detail/reference_content.hpp"
 #include "boost/none.hpp"
 #include "boost/utility/compare_pointees.hpp"
+#include "boost/utility/in_place_factory.hpp"
 
 #include "boost/optional/optional_fwd.hpp"
 
@@ -571,6 +576,14 @@ class optional : public optional_detail::optional_base
         return *this ;
       }
 
+    void swap( optional & arg )
+      {
+        // allow for Koenig lookup
+        using std::swap ;
+        swap(*this, arg);
+      }
+
+
     // Returns a reference to the value if this is initialized, otherwise,
     // the behaviour is UNDEFINED
     // No-throw
@@ -878,44 +891,77 @@ namespace optional_detail {
 #define BOOST_OPTIONAL_STD_SWAP_INTRODUCED_AT_NS_SCOPE
 #endif
 
-// optional's swap:
-// If both are initialized, calls swap(T&, T&). If this swap throws, both will remain initialized but their values are now unspecified.
-// If only one is initialized, calls U.reset(*I), THEN I.reset().
-// If U.reset(*I) throws, both are left UNCHANGED (U is kept uinitialized and I is never reset)
-// If both are uninitialized, do nothing (no-throw)
-template
-inline
-void optional_swap ( optional& x, optional& y )
-{
-  if ( !x && !!y )
+  template struct swap_selector;
+
+  template<>
+  struct swap_selector
   {
-    x.reset(*y);
-    y.reset();
-  }
-  else if ( !!x && !y )
-  {
-    y.reset(*x);
-    x.reset();
-  }
-  else if ( !!x && !!y )
-  {
-// GCC > 3.2 and all other compilers have the using declaration at function scope (FLC)
+    template
+    static void optional_swap ( optional& x, optional& y )
+    {
+     bool hasX = x;
+     bool hasY = y;
+
+     if ( !hasX && !hasY )
+       return;
+
+     if( !hasX )
+         x = boost::in_place();
+     else if ( !hasY )
+         y = boost::in_place();
+
+   // GCC > 3.2 and all other compilers have the using declaration at function scope (FLC)
 #ifndef BOOST_OPTIONAL_STD_SWAP_INTRODUCED_AT_NS_SCOPE
-    // allow for Koenig lookup
-    using std::swap ;
+     // allow for Koenig lookup
+     using std::swap ;
 #endif
-    swap(*x,*y);
-  }
-}
+     swap(*x,*y);
+
+     if( !hasX )
+         y = boost::none ;
+     else if( !hasY )
+         x = boost::none ;
+    }
+  };
+
+  template<>
+  struct swap_selector
+  {
+    template
+    static void optional_swap ( optional& x, optional& y )
+    {
+      if ( !x && !!y )
+      {
+        x = *y;
+        y = boost::none ;
+      }
+      else if ( !!x && !y )
+      {
+        y = *x ;
+        x = boost::none ;
+      }
+      else if ( !!x && !!y )
+      {
+    // GCC > 3.2 and all other compilers have the using declaration at function scope (FLC)
+    #ifndef BOOST_OPTIONAL_STD_SWAP_INTRODUCED_AT_NS_SCOPE
+        // allow for Koenig lookup
+        using std::swap ;
+    #endif
+        swap(*x,*y);
+      }
+    }
+  };
 
 } // namespace optional_detail
 
+template
+struct optional_swap_should_use_default_constructor : has_nothrow_default_constructor {} ;
+
 template inline void swap ( optional& x, optional& y )
 {
-  optional_detail::optional_swap(x,y);
+  optional_detail::swap_selector::value>::optional_swap(x, y);
 }
 
-
 } // namespace boost
 
 #endif

From 1afed544db9c2ede9fe1dc4b514a669e81174b44 Mon Sep 17 00:00:00 2001
From: Niels Dekker 
Date: Fri, 25 Apr 2008 16:52:34 +0000
Subject: [PATCH 12/18] Added unit tests, testing optional swap improvements
 of revision [44766]

[SVN r44767]
---
 test/optional_test.cpp | 187 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 186 insertions(+), 1 deletion(-)

diff --git a/test/optional_test.cpp b/test/optional_test.cpp
index 02ed181..8c6811b 100644
--- a/test/optional_test.cpp
+++ b/test/optional_test.cpp
@@ -1,4 +1,4 @@
-// Copyright (C) 2003, Fernando Luis Cacciola Carballal.
+// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
 //
 // Use, modification, and distribution is subject to the Boost Software
 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
@@ -9,6 +9,9 @@
 // You are welcome to contact the author at:
 //  fernando_cacciola@hotmail.com
 //
+// Revisions:
+// 25 Apr 2008 (added more swap tests)
+//
 #include
 #include
 #include
@@ -16,6 +19,8 @@
 #define BOOST_ENABLE_ASSERT_HANDLER
 
 #include "boost/bind/apply.hpp" // Included just to test proper interaction with boost::apply<> as reported by Daniel Wallin
+#include "boost/mpl/bool.hpp"
+#include "boost/mpl/bool_fwd.hpp"  // For mpl::true_ and mpl::false_
 
 #include "boost/optional/optional.hpp"
 
@@ -927,6 +932,185 @@ void test_conversions2()
   BOOST_CHECK(*get(&opt1) == static_cast(f));
 }
 
+
+namespace optional_swap_test
+{
+  class default_ctor_exception : public std::exception {} ;
+  class copy_ctor_exception : public std::exception {} ;
+  class assignment_exception : public std::exception {} ;
+
+  //
+  // Base class for swap test classes.  Its assignment should not be called, when swapping
+  // optional objects.  (The default std::swap would do so.)
+  //
+  class base_class_with_forbidden_assignment
+  {
+  public:
+    base_class_with_forbidden_assignment & operator=(const base_class_with_forbidden_assignment &)
+    {
+      BOOST_CHECK(!"The assignment should not be used while swapping!");
+      throw assignment_exception();
+    }
+
+    virtual ~base_class_with_forbidden_assignment() {}
+  };
+
+  //
+  // Class without default constructor
+  //
+  class class_without_default_ctor : public base_class_with_forbidden_assignment
+  {
+  public:
+    char data;
+    explicit class_without_default_ctor(char arg) : data(arg) {}
+  };
+
+  //
+  // Class whose default constructor should not be used by optional::swap!
+  //
+  class class_whose_default_ctor_should_not_be_used : public base_class_with_forbidden_assignment
+  {
+  public:
+    char data;
+    explicit class_whose_default_ctor_should_not_be_used(char arg) : data(arg) {}
+
+    class_whose_default_ctor_should_not_be_used()
+    {
+      BOOST_CHECK(!"This default constructor should not be used while swapping!");
+      throw default_ctor_exception();
+    }
+  };
+
+  //
+  // Class whose default constructor should be used by optional::swap.
+  // Its copy constructor should be avoided!
+  //
+  class class_whose_default_ctor_should_be_used : public base_class_with_forbidden_assignment
+  {
+  public:
+    char data;
+    explicit class_whose_default_ctor_should_be_used(char arg) : data(arg) { }
+
+    class_whose_default_ctor_should_be_used() : data('\0') { }
+
+    class_whose_default_ctor_should_be_used(const class_whose_default_ctor_should_be_used &)
+    {
+      BOOST_CHECK(!"This copy constructor should not be used while swapping!");
+      throw copy_ctor_exception();
+    }
+  };
+
+  void swap(class_whose_default_ctor_should_not_be_used & lhs, class_whose_default_ctor_should_not_be_used & rhs)
+  {
+    std::swap(lhs.data, rhs.data);
+  }
+
+  void swap(class_whose_default_ctor_should_be_used & lhs, class_whose_default_ctor_should_be_used & rhs)
+  {
+    std::swap(lhs.data, rhs.data);
+  }
+
+  void swap(class_without_default_ctor & lhs, class_without_default_ctor & rhs)
+  {
+    std::swap(lhs.data, rhs.data);
+  }
+
+} // End of namespace optional_swap_test.
+
+namespace boost {
+
+  //
+  // Compile time tweaking on whether or not swap should use the default constructor:
+  //
+  template <> struct optional_swap_should_use_default_constructor<
+    ::optional_swap_test::class_whose_default_ctor_should_be_used> : mpl::true_ {} ;
+
+  template <> struct optional_swap_should_use_default_constructor<
+    ::optional_swap_test::class_whose_default_ctor_should_not_be_used> : mpl::false_ {} ;
+}
+
+
+//
+// Tests whether the swap function works properly for optional.
+// Assumes that T has one data member, of type char.
+// Returns true iff the test is passed.
+//
+template 
+bool test_swap_function( T const* )
+{
+  const boost::unit_test::counter_t counter_before_test = boost::minimal_test::errors_counter();
+  try
+  {
+    optional obj1;
+    optional obj2('a');
+
+    // Test if obj1 and obj2 are properly initialized.
+    BOOST_CHECK(!obj1);
+    BOOST_CHECK(!!obj2 && obj2->data == 'a');
+
+    // Call non-member swap
+    swap(obj1, obj2);
+
+    // Test if obj1 and obj2 are really swapped
+    BOOST_CHECK(!!obj1 && obj1->data == 'a');
+    BOOST_CHECK(!obj2);
+  }
+  catch(const std::exception &)
+  {
+    // The swap function should not throw, for our test cases.
+    return false ;
+  }
+  return boost::minimal_test::errors_counter() == counter_before_test ;
+}
+
+//
+// Tests whether the optional::swap member function works properly.
+// Assumes that T has one data member, of type char. 
+// Returns true iff the test is passed.
+//
+template 
+bool test_swap_member_function( T const* )
+{
+  const boost::unit_test::counter_t counter_before_test = boost::minimal_test::errors_counter();
+  try
+  {
+    optional obj1;
+    optional obj2('a');
+
+    // Test if obj1 and obj2 are properly initialized.
+    BOOST_CHECK(!obj1);
+    BOOST_CHECK(!!obj2 && obj2->data == 'a');
+
+    // Call member swap
+    obj1.swap(obj2);
+
+    // Test if obj1 and obj2 are really swapped
+    BOOST_CHECK(!!obj1 && obj1->data == 'a');
+    BOOST_CHECK(!obj2);
+  }
+  catch(const std::exception &)
+  {
+    // The optional::swap member function should not throw, for our test cases.
+    return false ;
+  }
+  return boost::minimal_test::errors_counter() == counter_before_test ;
+}
+
+
+//
+// Tests compile time tweaking of swap, by means of
+// optional_swap_should_use_default_constructor.
+//
+void test_swap_tweaking()
+{
+  BOOST_CHECK( test_swap_function( ARG(optional_swap_test::class_without_default_ctor) ) );
+  BOOST_CHECK( test_swap_function( ARG(optional_swap_test::class_whose_default_ctor_should_be_used) ) );
+  BOOST_CHECK( test_swap_function( ARG(optional_swap_test::class_whose_default_ctor_should_not_be_used) ) );
+  BOOST_CHECK( test_swap_member_function( ARG(optional_swap_test::class_without_default_ctor) ) );
+  BOOST_CHECK( test_swap_member_function( ARG(optional_swap_test::class_whose_default_ctor_should_be_used) ) );
+  BOOST_CHECK( test_swap_member_function( ARG(optional_swap_test::class_whose_default_ctor_should_not_be_used) ) );
+}
+
 int test_main( int, char* [] )
 {
   try
@@ -936,6 +1120,7 @@ int test_main( int, char* [] )
     test_no_implicit_conversions();
     test_conversions1();
     test_conversions2();
+    test_swap_tweaking();
   }
   catch ( ... )
   {

From 951b49f992d2ae205fedf7e6a254ad54c1ad6cc5 Mon Sep 17 00:00:00 2001
From: Daniel James 
Date: Sun, 27 Apr 2008 07:39:49 +0000
Subject: [PATCH 13/18] Merge in documentation fixes.  Apart from the change to
 optional's documenation Jamfile, which I included by mistake.

Fixes #1659, #1661, #1684, #1685, 1687, #1690, #1801

I wrote about this at:

http://lists.boost.org/Archives/boost/2008/04/136405.php

Merged revisions 44585-44806 via svnmerge from
https://svn.boost.org/svn/boost/branches/doc

........
  r44585 | danieljames | 2008-04-19 16:25:27 +0100 (Sat, 19 Apr 2008) | 2 lines

  Fix broken link to vacpp in bjam docs. Refs #1512
........
  r44586 | danieljames | 2008-04-19 16:27:36 +0100 (Sat, 19 Apr 2008) | 2 lines

  Fix broken link to bcpp in bjam docs. Refs #1513
........
  r44587 | danieljames | 2008-04-19 16:33:58 +0100 (Sat, 19 Apr 2008) | 2 lines

  DateTime documentation - Fix a link to the serialization library. Refs #1659
........
  r44588 | danieljames | 2008-04-19 16:35:36 +0100 (Sat, 19 Apr 2008) | 2 lines

  Fix some links in interprocess & intrusive. Refs #1661
........
  r44589 | danieljames | 2008-04-19 16:37:39 +0100 (Sat, 19 Apr 2008) | 2 lines

  Fix some links in the python docs. Refs #1684.
........
  r44590 | danieljames | 2008-04-19 16:38:29 +0100 (Sat, 19 Apr 2008) | 2 lines

  Work around a quickbook bug which is affecting the python docs. Refs #1684.
........
  r44591 | danieljames | 2008-04-19 16:39:34 +0100 (Sat, 19 Apr 2008) | 2 lines

  Fix a broken link in the numeric conversion docs. Refs #1685
........
  r44592 | danieljames | 2008-04-19 16:40:45 +0100 (Sat, 19 Apr 2008) | 2 lines

  Fix some links in the optional docs. Refs #1687
........
  r44593 | danieljames | 2008-04-19 16:42:09 +0100 (Sat, 19 Apr 2008) | 2 lines

  Fix link to the hash documentation from bimap. Refs #1690
........
  r44599 | danieljames | 2008-04-19 18:07:33 +0100 (Sat, 19 Apr 2008) | 2 lines

  Fix a typo in the format library. Refs #1801
........
  r44600 | danieljames | 2008-04-19 19:20:59 +0100 (Sat, 19 Apr 2008) | 1 line

  Initialise svnmerge.
........
  r44641 | danieljames | 2008-04-20 18:59:47 +0100 (Sun, 20 Apr 2008) | 2 lines

  Fix the lincense url in shared container iterator documentation.
........
  r44642 | danieljames | 2008-04-20 19:00:00 +0100 (Sun, 20 Apr 2008) | 2 lines

  Fix image link in the mpi documentation.
........
  r44643 | danieljames | 2008-04-20 19:00:11 +0100 (Sun, 20 Apr 2008) | 2 lines

  Fix a typo in the spirit docs.
........
  r44644 | danieljames | 2008-04-20 19:00:23 +0100 (Sun, 20 Apr 2008) | 2 lines

  Escape the slash so that quickbook doesn't think it the start of an italic section, and mess up the link. Refs #1844
........
  r44647 | danieljames | 2008-04-20 19:39:47 +0100 (Sun, 20 Apr 2008) | 2 lines

  Fix another typo in spirit docs.
........


[SVN r44807]
---
 doc/optional.qbk | 2 +-
 index.html       | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/doc/optional.qbk b/doc/optional.qbk
index 7388b5f..5217e49 100644
--- a/doc/optional.qbk
+++ b/doc/optional.qbk
@@ -22,7 +22,7 @@ Distributed under the Boost Software License, Version 1.0.
 [/ Cited Boost resources ]
 
 [def __BOOST_VARIANT__ [@../../../variant/index.html Boost.Variant]]
-[def __BOOST_TRIBOOL__ [@../../../tribool/index.html boost::tribool]]
+[def __BOOST_TRIBOOL__ [@../../../../doc/html/tribool.html boost::tribool]]
 
 [def __OPTIONAL_POINTEE__ [@../../../utility/OptionalPointee.html OptionalPointee]]
 [def __COPY_CONSTRUCTIBLE__ [@../../../utility/CopyConstructible.html Copy Constructible]]
diff --git a/index.html b/index.html
index 3031e05..84b7c93 100644
--- a/index.html
+++ b/index.html
@@ -4,10 +4,10 @@
 
 
 Automatic redirection failed, please go to
-doc/html/index.html. 
    
+doc/html/index.html. 
    
 
    � Copyright Beman Dawes, 2001
    
 
    Distributed under the Boost Software License, Version 1.0. (See accompanying 
 file LICENSE_1_0.txt or copy 
 at www.boost.org/LICENSE_1_0.txt)
    
 
-
\ No newline at end of file
+

From a4572497bef424f4db0ceb4fe75661ce0218611a Mon Sep 17 00:00:00 2001
From: Niels Dekker 
Date: Sun, 27 Apr 2008 21:07:10 +0000
Subject: [PATCH 14/18] Added forward declaration of optional's boost::swap
 overload, as mentioned at
 http://article.gmane.org/gmane.comp.lib.boost.devel/174350 "Re: [optional]
 problems with swap()"

[SVN r44825]
---
 include/boost/optional/optional_fwd.hpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/boost/optional/optional_fwd.hpp b/include/boost/optional/optional_fwd.hpp
index 2cf4fa6..f36bebf 100644
--- a/include/boost/optional/optional_fwd.hpp
+++ b/include/boost/optional/optional_fwd.hpp
@@ -1,4 +1,4 @@
-// Copyright (C) 2003, Fernando Luis Cacciola Carballal.
+// Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
 //
 // Use, modification, and distribution is subject to the Boost Software
 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
@@ -9,6 +9,9 @@
 // You are welcome to contact the author at:
 //  fernando_cacciola@hotmail.com
 //
+// Revisions:
+// 27 Apr 2008 (added forward declaration of boost::swap overload) Niels Dekker
+// 
 #ifndef BOOST_OPTIONAL_OPTIONAL_FWD_FLC_19NOV2002_HPP
 #define BOOST_OPTIONAL_OPTIONAL_FWD_FLC_19NOV2002_HPP
 
@@ -16,6 +19,8 @@ namespace boost {
 
 template class optional ;
 
+template void swap ( optional& , optional& ) ;
+
 } // namespace boost
 
 #endif

From 74674531c880f34773ecfc9c89e7198b84e6fd72 Mon Sep 17 00:00:00 2001
From: Niels Dekker 
Date: Sun, 27 Apr 2008 21:09:50 +0000
Subject: [PATCH 15/18] Replaced "using std::swap" by "using boost::swap"
 within optional::swap member function, hoping to fix GCC test failures, as
 mentioned at http://article.gmane.org/gmane.comp.lib.boost.devel/174350 "Re:
 [optional] problems with swap()"

[SVN r44826]
---
 include/boost/optional/optional.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/boost/optional/optional.hpp b/include/boost/optional/optional.hpp
index f23df09..01db469 100644
--- a/include/boost/optional/optional.hpp
+++ b/include/boost/optional/optional.hpp
@@ -10,7 +10,7 @@
 //  fernando_cacciola@hotmail.com
 //
 // Revisions:
-// 25 Apr 2008 (improved swap) Fernando Cacciola, Niels Dekker, Thorsten Ottosen
+// 27 Apr 2008 (improved swap) Fernando Cacciola, Niels Dekker, Thorsten Ottosen
 // 
 #ifndef BOOST_OPTIONAL_OPTIONAL_FLC_19NOV2002_HPP
 #define BOOST_OPTIONAL_OPTIONAL_FLC_19NOV2002_HPP
@@ -579,7 +579,7 @@ class optional : public optional_detail::optional_base
     void swap( optional & arg )
       {
         // allow for Koenig lookup
-        using std::swap ;
+        using boost::swap ;
         swap(*this, arg);
       }
 

From 43eac5bb126413fdc31ba04c18b79dda3c6b603f Mon Sep 17 00:00:00 2001
From: Niels Dekker 
Date: Sat, 10 May 2008 14:42:49 +0000
Subject: [PATCH 16/18] Added forward declaration of
 boost::optional_swap_should_use_default_constructor.

[SVN r45264]
---
 include/boost/optional/optional_fwd.hpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/boost/optional/optional_fwd.hpp b/include/boost/optional/optional_fwd.hpp
index f36bebf..a74fe10 100644
--- a/include/boost/optional/optional_fwd.hpp
+++ b/include/boost/optional/optional_fwd.hpp
@@ -10,7 +10,7 @@
 //  fernando_cacciola@hotmail.com
 //
 // Revisions:
-// 27 Apr 2008 (added forward declaration of boost::swap overload) Niels Dekker
+// 10 May 2008 (added swap related forward declaration) Niels Dekker
 // 
 #ifndef BOOST_OPTIONAL_OPTIONAL_FWD_FLC_19NOV2002_HPP
 #define BOOST_OPTIONAL_OPTIONAL_FWD_FLC_19NOV2002_HPP
@@ -21,6 +21,8 @@ template class optional ;
 
 template void swap ( optional& , optional& ) ;
 
+template struct optional_swap_should_use_default_constructor ;
+
 } // namespace boost
 
 #endif

From 63f6e7f45e7cdae40d389881c82e234fa4bd4e81 Mon Sep 17 00:00:00 2001
From: Niels Dekker 
Date: Sat, 10 May 2008 14:53:51 +0000
Subject: [PATCH 17/18] Added more optional::swap tests, especially on self
 swap, on specializing boost::swap for optional, and on swapping
 optional when T is a template class.

[SVN r45265]
---
 test/optional_test.cpp | 167 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 152 insertions(+), 15 deletions(-)

diff --git a/test/optional_test.cpp b/test/optional_test.cpp
index 8c6811b..a2c9df9 100644
--- a/test/optional_test.cpp
+++ b/test/optional_test.cpp
@@ -10,7 +10,7 @@
 //  fernando_cacciola@hotmail.com
 //
 // Revisions:
-// 25 Apr 2008 (added more swap tests)
+// 10 May 2008 (added more swap tests)
 //
 #include
 #include
@@ -1000,6 +1000,49 @@ namespace optional_swap_test
     }
   };
 
+  //
+  // Class template whose default constructor should be used by optional::swap.
+  // Its copy constructor should be avoided!
+  //
+  template 
+  class template_whose_default_ctor_should_be_used : public base_class_with_forbidden_assignment
+  {
+  public:
+    T data;
+    explicit template_whose_default_ctor_should_be_used(T arg) : data(arg) { }
+
+    template_whose_default_ctor_should_be_used() : data('\0') { }
+
+    template_whose_default_ctor_should_be_used(const template_whose_default_ctor_should_be_used &)
+    {
+      BOOST_CHECK(!"This copy constructor should not be used while swapping!");
+      throw copy_ctor_exception();
+    }
+  };
+
+  //
+  // Class whose explicit constructor should be used by optional::swap.
+  // Its other constructors should be avoided!
+  //
+  class class_whose_explicit_ctor_should_be_used : public base_class_with_forbidden_assignment
+  {
+  public:
+    char data;
+    explicit class_whose_explicit_ctor_should_be_used(char arg) : data(arg) { }
+
+    class_whose_explicit_ctor_should_be_used()
+    {
+      BOOST_CHECK(!"This default constructor should not be used while swapping!");
+      throw default_ctor_exception();
+    }
+
+    class_whose_explicit_ctor_should_be_used(const class_whose_explicit_ctor_should_be_used &)
+    {
+      BOOST_CHECK(!"This copy constructor should not be used while swapping!");
+      throw copy_ctor_exception();
+    }
+  };
+
   void swap(class_whose_default_ctor_should_not_be_used & lhs, class_whose_default_ctor_should_not_be_used & rhs)
   {
     std::swap(lhs.data, rhs.data);
@@ -1015,18 +1058,90 @@ namespace optional_swap_test
     std::swap(lhs.data, rhs.data);
   }
 
+  void swap(class_whose_explicit_ctor_should_be_used & lhs, class_whose_explicit_ctor_should_be_used & rhs)
+  {
+    std::swap(lhs.data, rhs.data);
+  }
+
+  template 
+  void swap(template_whose_default_ctor_should_be_used & lhs, template_whose_default_ctor_should_be_used & rhs)
+  {
+    std::swap(lhs.data, rhs.data);
+  }
+
+  //
+  // optional::swap should be customized when neither the copy constructor
+  // nor the default constructor of T are supposed to be used when swapping, e.g.,
+  // for the following type T = class_whose_explicit_ctor_should_be_used.
+  //
+  void swap(boost::optional & x, boost::optional & y)
+  {
+    bool hasX = x;
+    bool hasY = y;
+
+    if ( !hasX && !hasY )
+     return;
+
+    if( !hasX )
+       x = boost::in_place('\0');
+    else if ( !hasY )
+       y = boost::in_place('\0');
+    
+    optional_swap_test::swap(*x,*y);
+
+     if( !hasX )
+         y = boost::none ;
+     else if( !hasY )
+         x = boost::none ;
+  }
+
+
 } // End of namespace optional_swap_test.
 
-namespace boost {
 
-  //
-  // Compile time tweaking on whether or not swap should use the default constructor:
-  //
-  template <> struct optional_swap_should_use_default_constructor<
-    ::optional_swap_test::class_whose_default_ctor_should_be_used> : mpl::true_ {} ;
+//
+// Compile time tweaking on whether or not swap should use the default constructor:
+//
+template <> struct boost::optional_swap_should_use_default_constructor<
+  optional_swap_test::class_whose_default_ctor_should_be_used> : boost::mpl::true_ {} ;
 
-  template <> struct optional_swap_should_use_default_constructor<
-    ::optional_swap_test::class_whose_default_ctor_should_not_be_used> : mpl::false_ {} ;
+template <> struct boost::optional_swap_should_use_default_constructor<
+  optional_swap_test::class_whose_default_ctor_should_not_be_used> : boost::mpl::false_ {} ;
+
+template  struct boost::optional_swap_should_use_default_constructor<
+  optional_swap_test::template_whose_default_ctor_should_be_used > : boost::mpl::true_ {} ;
+
+//
+// Swap specializations:
+//
+template <> 
+void boost::swap(boost::optional & x, boost::optional & y)
+{
+  optional_swap_test::swap(x, y);
+}
+
+template <> 
+void std::swap(optional_swap_test::class_whose_default_ctor_should_be_used & x, optional_swap_test::class_whose_default_ctor_should_be_used & y)
+{
+  optional_swap_test::swap(x, y);
+}
+
+template <> 
+void std::swap(optional_swap_test::class_whose_default_ctor_should_not_be_used & x, optional_swap_test::class_whose_default_ctor_should_not_be_used & y)
+{
+  optional_swap_test::swap(x, y);
+}
+
+template <> 
+void std::swap(optional_swap_test::class_without_default_ctor & x, optional_swap_test::class_without_default_ctor & y)
+{
+  optional_swap_test::swap(x, y);
+}
+
+template <> 
+void std::swap(optional_swap_test::class_whose_explicit_ctor_should_be_used & x, optional_swap_test::class_whose_explicit_ctor_should_be_used & y)
+{
+  optional_swap_test::swap(x, y);
 }
 
 
@@ -1044,16 +1159,25 @@ bool test_swap_function( T const* )
     optional obj1;
     optional obj2('a');
 
-    // Test if obj1 and obj2 are properly initialized.
+    // Self-swap should not have any effect.
+    swap(obj1, obj1);
+    swap(obj2, obj2);
     BOOST_CHECK(!obj1);
     BOOST_CHECK(!!obj2 && obj2->data == 'a');
 
-    // Call non-member swap
+    // Call non-member swap.
     swap(obj1, obj2);
 
-    // Test if obj1 and obj2 are really swapped
+    // Test if obj1 and obj2 are really swapped.
     BOOST_CHECK(!!obj1 && obj1->data == 'a');
     BOOST_CHECK(!obj2);
+
+    // Call non-member swap one more time.
+    swap(obj1, obj2);
+
+    // Test if obj1 and obj2 are swapped back.
+    BOOST_CHECK(!obj1);
+    BOOST_CHECK(!!obj2 && obj2->data == 'a');
   }
   catch(const std::exception &)
   {
@@ -1077,16 +1201,25 @@ bool test_swap_member_function( T const* )
     optional obj1;
     optional obj2('a');
 
-    // Test if obj1 and obj2 are properly initialized.
+    // Self-swap should not have any effect.
+    obj1.swap(obj1);
+    obj2.swap(obj2);
     BOOST_CHECK(!obj1);
     BOOST_CHECK(!!obj2 && obj2->data == 'a');
 
-    // Call member swap
+    // Call member swap.
     obj1.swap(obj2);
 
-    // Test if obj1 and obj2 are really swapped
+    // Test if obj1 and obj2 are really swapped.
     BOOST_CHECK(!!obj1 && obj1->data == 'a');
     BOOST_CHECK(!obj2);
+
+    // Call member swap one more time.
+    obj1.swap(obj2);
+
+    // Test if obj1 and obj2 are swapped back.
+    BOOST_CHECK(!obj1);
+    BOOST_CHECK(!!obj2 && obj2->data == 'a');
   }
   catch(const std::exception &)
   {
@@ -1106,9 +1239,13 @@ void test_swap_tweaking()
   BOOST_CHECK( test_swap_function( ARG(optional_swap_test::class_without_default_ctor) ) );
   BOOST_CHECK( test_swap_function( ARG(optional_swap_test::class_whose_default_ctor_should_be_used) ) );
   BOOST_CHECK( test_swap_function( ARG(optional_swap_test::class_whose_default_ctor_should_not_be_used) ) );
+  BOOST_CHECK( test_swap_function( ARG(optional_swap_test::class_whose_explicit_ctor_should_be_used) ) );
+  BOOST_CHECK( test_swap_function( ARG(optional_swap_test::template_whose_default_ctor_should_be_used) ) );
   BOOST_CHECK( test_swap_member_function( ARG(optional_swap_test::class_without_default_ctor) ) );
   BOOST_CHECK( test_swap_member_function( ARG(optional_swap_test::class_whose_default_ctor_should_be_used) ) );
   BOOST_CHECK( test_swap_member_function( ARG(optional_swap_test::class_whose_default_ctor_should_not_be_used) ) );
+  BOOST_CHECK( test_swap_member_function( ARG(optional_swap_test::class_whose_explicit_ctor_should_be_used) ) );
+  BOOST_CHECK( test_swap_member_function( ARG(optional_swap_test::template_whose_default_ctor_should_be_used) ) );
 }
 
 int test_main( int, char* [] )

From 3ebabcb2d8dcb410544aa6d67b3d2011c5163c6f Mon Sep 17 00:00:00 2001
From: Niels Dekker 
Date: Mon, 12 May 2008 13:29:52 +0000
Subject: [PATCH 18/18] Fixed syntax of
 optional_swap_should_use_default_constructor and swap template
 specializations that I added 2 days ago (changeset [45265]). Was accepted by
 MSVC, but rejected by other compilers.

[SVN r45295]
---
 test/optional_test.cpp | 49 +++++++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 17 deletions(-)

diff --git a/test/optional_test.cpp b/test/optional_test.cpp
index a2c9df9..e841194 100644
--- a/test/optional_test.cpp
+++ b/test/optional_test.cpp
@@ -10,7 +10,7 @@
 //  fernando_cacciola@hotmail.com
 //
 // Revisions:
-// 10 May 2008 (added more swap tests)
+// 12 May 2008 (added more swap tests)
 //
 #include
 #include
@@ -1099,50 +1099,65 @@ namespace optional_swap_test
 } // End of namespace optional_swap_test.
 
 
+namespace boost {
+
 //
 // Compile time tweaking on whether or not swap should use the default constructor:
 //
-template <> struct boost::optional_swap_should_use_default_constructor<
-  optional_swap_test::class_whose_default_ctor_should_be_used> : boost::mpl::true_ {} ;
 
-template <> struct boost::optional_swap_should_use_default_constructor<
-  optional_swap_test::class_whose_default_ctor_should_not_be_used> : boost::mpl::false_ {} ;
+template <> struct optional_swap_should_use_default_constructor<
+  optional_swap_test::class_whose_default_ctor_should_be_used> : mpl::true_ {} ;
+
+template <> struct optional_swap_should_use_default_constructor<
+  optional_swap_test::class_whose_default_ctor_should_not_be_used> : mpl::false_ {} ;
+
+template  struct optional_swap_should_use_default_constructor<
+  optional_swap_test::template_whose_default_ctor_should_be_used > : mpl::true_ {} ;
 
-template  struct boost::optional_swap_should_use_default_constructor<
-  optional_swap_test::template_whose_default_ctor_should_be_used > : boost::mpl::true_ {} ;
 
 //
-// Swap specializations:
+// Specialization of boost::swap:
 //
 template <> 
-void boost::swap(boost::optional & x, boost::optional & y)
+void swap(optional & x, optional & y)
+{
+  optional_swap_test::swap(x, y);
+}
+
+} // namespace boost
+
+
+namespace std {
+
+//
+// Specializations of std::swap:
+//
+
+template <> 
+void swap(optional_swap_test::class_whose_default_ctor_should_be_used & x, optional_swap_test::class_whose_default_ctor_should_be_used & y)
 {
   optional_swap_test::swap(x, y);
 }
 
 template <> 
-void std::swap(optional_swap_test::class_whose_default_ctor_should_be_used & x, optional_swap_test::class_whose_default_ctor_should_be_used & y)
+void swap(optional_swap_test::class_whose_default_ctor_should_not_be_used & x, optional_swap_test::class_whose_default_ctor_should_not_be_used & y)
 {
   optional_swap_test::swap(x, y);
 }
 
 template <> 
-void std::swap(optional_swap_test::class_whose_default_ctor_should_not_be_used & x, optional_swap_test::class_whose_default_ctor_should_not_be_used & y)
+void swap(optional_swap_test::class_without_default_ctor & x, optional_swap_test::class_without_default_ctor & y)
 {
   optional_swap_test::swap(x, y);
 }
 
 template <> 
-void std::swap(optional_swap_test::class_without_default_ctor & x, optional_swap_test::class_without_default_ctor & y)
+void swap(optional_swap_test::class_whose_explicit_ctor_should_be_used & x, optional_swap_test::class_whose_explicit_ctor_should_be_used & y)
 {
   optional_swap_test::swap(x, y);
 }
 
-template <> 
-void std::swap(optional_swap_test::class_whose_explicit_ctor_should_be_used & x, optional_swap_test::class_whose_explicit_ctor_should_be_used & y)
-{
-  optional_swap_test::swap(x, y);
-}
+} // namespace std
 
 
 //