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New smart pointer documentation. Related clean-up of the smart pointer

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library. Changing includes to include the new individual smart pointer
headers. Replacing old smart pointer library with an include of the new
smart pointer headers. Simplify ifdefs that involve the member templates
macros now that BOOST_MSVC6_MEMBER_TEMPLATES is also guaranteed to bet
set for platforms that have full member templates.


[SVN r12647]
This commit is contained in:
Darin Adler
2002-02-02 18:36:12 +00:00
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commit 1a7cd887e4
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<h1><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="center" width="277" height="86">Class
<a name="shared_array">shared_array</a></h1>
<p>Class <strong>shared_array</strong> stores a pointer to a dynamically
allocated array. (Dynamically allocated arrays are allocated with the C++ <tt>new[]</tt>
expression.)&nbsp;&nbsp; The array pointed to is guaranteed to be deleted,
either on destruction of the <strong>shared_array</strong>, on <strong>shared_array::operator=()</strong>,
or via an explicit <strong>shared_array::reset()</strong>.&nbsp; See <a href="#shared_array_example">example</a>.</p>
<p>Class<strong> shared_array</strong> meets the <strong>CopyConstuctible</strong>
and <strong>Assignable</strong> requirements of the C++ Standard Library, and so
can be used in C++ Standard Library containers.&nbsp; A specialization of std::
less&lt; &gt; for&nbsp; boost::shared_ptr&lt;Y&gt; is supplied so that&nbsp;<strong>
shared_array</strong> works by default for Standard Library's Associative
Container Compare template parameter.&nbsp; For compilers not supporting partial
specialization, the user must explicitly pass the less&lt;&gt; functor.</p>
<p>Class<strong> shared_array</strong> cannot correctly hold a pointer to a
single object.&nbsp; See <a href="shared_ptr.htm"><strong>shared_ptr</strong></a>
<h1><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="middle" width="277" height="86">shared_array class template</h1>
<p>The <b>shared_array</b> class template stores a pointer to a dynamically allocated
array. (Dynamically allocated array are allocated with the C++ <b>new[]</b>
expression.) The object pointed to is guaranteed to be deleted when
the last <b>shared_array</b> pointing to it is destroyed or reset.</p>
<p>Every <b>shared_array</b> meets the <b>CopyConstructible</b>
and <b>Assignable</b> requirements of the C++ Standard Library, and so
can be used in standard library containers. Comparison operators
are supplied so that <b>shared_array</b> works with
the standard library's associative containers.</p>
<p>Normally, a <b>shared_array</b> cannot correctly hold a pointer to a
dynamically allocated array. See <a href="shared_ptr.htm"><b>shared_ptr</b></a>
for that usage.</p>
<p>Class<strong> shared_array</strong> will not work correctly with cyclic data
structures. For example, if main() holds a shared_array pointing to array A,
which directly or indirectly holds a shared_array pointing back to array A, then
array A's use_count() will be 2, and destruction of the main() shared_array will
leave array A dangling with a use_count() of 1.</p>
<p>A C++ Standard Library <strong>vector</strong> is <strong> </strong>a <strong>
</strong>heavier duty alternative to a <strong>shared_array</strong>.</p>
<p>The class is a template parameterized on <tt>T</tt>, the type of the object
pointed to.&nbsp;&nbsp; <tt>T</tt> must meet the smart pointer <a href="smart_ptr.htm#Common requirements">Common
requirements</a>.</p>
<h2>Class shared_array Synopsis</h2>
<pre>#include &lt;<a href="../../boost/smart_ptr.hpp">boost/smart_ptr.hpp</a>&gt;
namespace boost {
template&lt;typename T&gt; class shared_array {
<p>Because the implementation uses reference counting, <b>shared_array</b> will not work
correctly with cyclic data structures. For example, if <b>main()</b> holds a <b>shared_array</b>
to <b>A</b>, which directly or indirectly holds a <b>shared_array</b> back to <b>A</b>,
<b>A</b>'s use count will be 2. Destruction of the original <b>shared_array</b>
will leave <b>A</b> dangling with a use count of 1.</p>
public:
typedef T <a href="#shared_array_element_type">element_type</a>;
<p>A <b>shared_ptr</b> to a <b>std::vector</b> is an alternative to a <b>shared_array</b> that is
a bit heavier duty but far more flexible.</p>
explicit <a href="#shared_array_ctor">shared_array</a>( T* p=0 );
<a href="#shared_array_ctor">shared_array</a>( const shared_array&amp; ); // never throws
<strong> </strong><a href="#shared_array_~shared_array">~shared_array</a>();
<p>The class template is parameterized on <b>T</b>, the type of the object
pointed to. <b>T</b> must meet the smart pointer
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
shared_array&amp; <a href="#shared_array_operator=">operator=</a>( const shared_array&amp; ); // never throws
<h2>Synopsis</h2>
void <a href="#shared_array_reset">reset</a>( T* p=0 );
<pre>namespace boost {
T&amp; <a href="#shared_array_operator[]">operator[]</a>(std::size_t i) const; // never throws
T* <a href="#shared_array_get">get</a>() const; // never throws
template&lt;typename T&gt; class shared_array {
long <a href="#shared_array_use_count">use_count</a>() const; // never throws
bool <a href="#shared_array_unique">unique</a>() const; // never throws
public:
typedef T <a href="#element_type">element_type</a>;
void <a href="#shared_array_swap">swap</a>( shared_array&lt;T&gt;&amp; other ) throw()
};
explicit <a href="#constructors">shared_array</a>(T * p = 0);
template&lt;typename D&gt; <a href="#constructors">shared_array</a>(T * p, D d);
<a href="#destructor">~shared_array</a>(); // never throws
template&lt;typename T&gt;
inline bool operator==(const shared_array&lt;T&gt;&amp; a, const shared_array&lt;T&gt;&amp; b)
{ return a.get() == b.get(); }
<a href="#constructors">shared_array</a>(shared_array const &amp; r); // never throws
template&lt;typename T&gt;
inline bool operator!=(const shared_array&lt;T&gt;&amp; a, const shared_array&lt;T&gt;&amp; b)
{ return a.get() != b.get(); }
}</pre>
<pre>namespace std {
shared_array &amp; <a href="#assignment">operator=</a>(shared_array const &amp; r); // never throws
template&lt;typename T&gt;
inline void swap(boost::shared_array&lt;T&gt;&amp; a, boost::shared_array&lt;T&gt;&amp; b)
{ a.swap(b); }
void <a href="#reset">reset</a>(T * p = 0); // never throws
template&lt;typename D&gt; void <a href="#reset">reset</a>(T * p, D d); // never throws
template&lt;typename T&gt;
struct less&lt; boost::shared_array&lt;T&gt; &gt;
: binary_function&lt;boost::shared_array&lt;T&gt;, boost::shared_array&lt;T&gt;, bool&gt;
{
bool operator()(const boost::shared_array&lt;T&gt;&amp; a,
const boost::shared_array&lt;T&gt;&amp; b) const
{ return less&lt;T*&gt;()(a.get(),b.get()); }
T &amp; <a href="#indexing">operator[]</a>(std::ptrdiff_t i) const() const; // never throws
T * <a href="#get">get</a>() const; // never throws
bool <a href="#unique">unique</a>() const; // never throws
long <a href="#use_count">use_count</a>() const; // never throws
void <a href="#swap">swap</a>(shared_array&lt;T&gt; &amp; b); // never throws
};
} // namespace std </pre>
<p>Specialization of std::swap uses the fast, non-throwing swap that's provided
as a member function instead of using the default algorithm which creates a
temporary and uses assignment.<br>
<br>
Specialization of std::less allows use of shared arrays as keys in&nbsp;C++
Standard Library associative collections.<br>
<br>
The std::less specializations use std::less&lt;T*&gt; to perform the
comparison.&nbsp; This insures that pointers are handled correctly, since the
standard mandates that relational operations on pointers are unspecified (5.9 [expr.rel]
paragraph 2) but std::less&lt;&gt; on pointers is well-defined (20.3.3 [lib.comparisons]
paragraph 8).<br>
<br>
It's still a controversial question whether supplying only std::less is better
than supplying a full range of comparison operators (&lt;, &gt;, &lt;=, &gt;=).</p>
<p>The current implementation does not supply the specializations if the macro
name BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION is defined.</p>
<h2>Class shared_array Members</h2>
<h3>shared_array <a name="shared_array_element_type">element_type</a></h3>
template&lt;typename T&gt;
bool <a href="#operator==">operator==</a>(shared_array&lt;T&gt; const &amp; a, shared_array&lt;T&gt; const &amp; b); // never throws
template&lt;typename T&gt;
bool <a href="#operator!=">operator!=</a>(shared_array&lt;T&gt; const &amp; a, shared_array&lt;T&gt; const &amp; b); // never throws
template&lt;typename T&gt;
bool <a href="#operator&lt;">operator&lt;</a>(shared_array&lt;T&gt; const &amp; a, shared_array&lt;T&gt; const &amp; b); // never throws
template&lt;typename T&gt; void <a href="#free-swap">swap</a>(shared_array&lt;T&gt; &amp; a, shared_array&lt;T&gt; &amp; b); // never throws
}</pre>
<h2>Members</h2>
<h3><a name="element_type">element_type</a></h3>
<pre>typedef T element_type;</pre>
<p>Provides the type of the stored pointer.</p>
<h3><a name="shared_array_ctor">shared_array constructors</a></h3>
<pre>explicit shared_array( T* p=0 );</pre>
<p>Constructs a <strong>shared_array</strong>, storing a copy of <tt>p</tt>,
which must have been allocated via a C++ <tt>new</tt>[] expression or be 0.
Afterwards, use_count() is 1 (even if p==0; see <a href="#shared_array_~shared_array">~shared_array</a>).</p>
<p>The only exception which may be thrown is <tt>std::bad_alloc</tt>.&nbsp; If
an exception is thrown,&nbsp; <tt>delete[] p</tt> is called.</p>
<pre>shared_array( const shared_array&amp; r); // never throws</pre>
<p>Constructs a <strong>shared_array</strong>, as if by storing a copy of the
pointer stored in <strong>r</strong>. Afterwards, <strong>use_count()</strong>
for all copies is 1 more than the initial <strong>r.use_count()</strong>.</p>
<h3><a name="shared_array_~shared_array">shared_array destructor</a></h3>
<pre>~shared_array();</pre>
<p>If <strong>use_count()</strong> == 1, deletes the array pointed to by the
stored pointer.&nbsp;Otherwise, <strong>use_count()</strong> for any remaining
copies is decremented by 1. Note that in C++ <tt>delete</tt>[] on a pointer with
a value of 0 is harmless.</p>
<p>Does not throw exceptions.</p>
<h3>shared_array <a name="shared_array_operator=">operator=</a></h3>
<pre>shared_array&amp; operator=( const shared_array&amp; r); // never throws</pre>
<p>First, if <strong>use_count()</strong> == 1, deletes the array pointed to by
the stored pointer.&nbsp;Otherwise, <strong>use_count()</strong> for any
remaining copies is decremented by 1. Note that in C++ <tt>delete</tt>[] on a
pointer with a value of 0 is harmless.</p>
<p>Then replaces the contents of <strong>this</strong>, as if by storing a copy
of the pointer stored in <strong>r</strong>. Afterwards, <strong>use_count()</strong>
for all copies is 1 more than the initial <strong>r.use_count()</strong>.&nbsp;</p>
<h3>shared_array <a name="shared_array_reset">reset</a></h3>
<pre>void reset( T* p=0 );</pre>
<p>First, if <strong>use_count()</strong> == 1, deletes the array pointed to by
the stored pointer.&nbsp;Otherwise, <strong>use_count()</strong> for any
remaining copies is decremented by 1. Note that in C++&nbsp; <tt>delete</tt>[]
on a pointer with a value of 0 is harmless.</p>
<p>Then replaces the contents of <strong>this</strong>, as if by storing a copy
of <strong>p</strong>, which must have been allocated via a C++ <tt>new</tt>[]
expression or be 0. Afterwards, <strong>use_count()</strong> is 1 (even if p==0;
see <a href="#shared_array_~shared_array">~shared_array</a>).</p>
<p>The only exception which may be thrown is <tt>std::bad_alloc</tt>.&nbsp; If
an exception is thrown,&nbsp; <tt>delete[] p</tt> is called.</p>
<h3>shared_array <a name="shared_array_operator[]">operator[]</a></h3>
<p><tt>T&amp; operator[](std::size_t i) const; // never throws</tt></p>
<p>Returns a reference to element <tt>i</tt> of the array pointed to by the
stored pointer.</p>
<p>Behavior is undefined (and almost certainly undesirable) if <tt>get()==0</tt>,
or if <tt>i</tt> is less than 0 or is greater or equal to the number of elements
<h3><a name="constructors">constructors</a></h3>
<pre>explicit shared_array(T * p = 0);</pre>
<p>Constructs a <b>shared_array</b>, storing a copy of <b>p</b>, which
must be a pointer to an array that was allocated via a C++ <b>new[]</b> expression or be 0.
Afterwards, the <a href="#use_count">use count</a> is 1 (even if p == 0; see <a href="#destructor">~shared_array</a>).
The only exception which may be thrown by this constructor is <b>std::bad_alloc</b>.
If an exception is thrown, <b>delete[] p</b> is called.</p>
<pre>template&lt;typename D&gt; shared_array(T * p, D d);</pre>
<p>Constructs a <b>shared_array</b>, storing a copy of <b>p</b> and of <b>d</b>.
Afterwards, the <a href="#use_count">use count</a> is 1.
<b>D</b>'s copy constructor must not throw.
When the the time comes to delete the array pointed to by <b>p</b>, the object
<b>d</b> is used in the statement <b>d(p)</b>. Invoking the object <b>d</b> with
parameter <b>p</b> in this way must not throw.
The only exception which may be thrown by this constructor is <b>std::bad_alloc</b>.
If an exception is thrown, <b>d(p)</b> is called.</p>
<pre>shared_array(shared_array const &amp; r); // never throws</pre>
<p>Constructs a <b>shared_array</b>, as if by storing a copy of the
pointer stored in <b>r</b>. Afterwards, the <a href="#use_count">use count</a>
for all copies is 1 more than the initial use count.</p>
<h3><a name="destructor">destructor</a></h3>
<pre>~shared_array(); // never throws</pre>
<p>Decrements the <a href="#use_count">use count</a>. Then, if the use count is 0,
deletes the array pointed to by the stored pointer.
Note that <b>delete[]</b> on a pointer with a value of 0 is harmless.
<b>T</b> need not be a complete type.
The guarantee that this does not throw exceptions depends on the requirement that the
deleted object's destructor does not throw exceptions.
See the smart pointer <a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
<h3><a name="operator=">assignment</a></h3>
<pre>shared_array &amp; <a href="#assignment">operator=</a>(shared_array const &amp; r); // never throws</pre>
<p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>,
then replaces this <b>shared_array</b> with the new one, destroying the replaced object.</p>
<h3><a name="reset">reset</a></h3>
<pre>void reset(T * p = 0);</pre>
<p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>,
then replaces this <b>shared_array</b> with the new one, destroying the replaced object.
The only exception which may be thrown is <b>std::bad_alloc</b>. If
an exception is thrown, <b>delete[] p</b> is called.</p>
<pre>template&lt;typename D&gt; void reset(T * p, D d);</pre>
<p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>,
then replaces this <b>shared_array</b> with the new one, destroying the replaced object.
<b>D</b>'s copy constructor must not throw.
The only exception which may be thrown is <b>std::bad_alloc</b>. If
an exception is thrown, <b>d(p)</b> is called.</p>
<h3><a name="indirection">indexing</a></h3>
<pre>T &amp; operator[](std::size_t i) const; // never throws</pre>
<p>Returns a reference to element <b>i</b> of the array pointed to by the stored pointer.
Behavior is undefined and almost certainly undesirable if the stored pointer is 0,
or if <b>i</b> is less than 0 or is greater than or equal to the number of elements
in the array.</p>
<h3>shared_array <a name="shared_array_get">get</a></h3>
<pre>T* get() const; // never throws</pre>
<p><b>T</b> is not required be a complete type.&nbsp;
See <a href="smart_ptr.htm#Common requirements">Common Requirements</a>.</p>
<p>Returns the stored pointer.</p>
<h3>shared_array<a name="shared_array_use_count"> use_count</a></h3>
<p><tt>long use_count() const; // never throws</tt></p>
<p><b>T</b> is not required be a complete type.&nbsp;
See <a href="smart_ptr.htm#Common requirements">Common Requirements</a>.</p>
<p>Returns the number of <strong>shared_arrays</strong> sharing ownership of the
stored pointer.</p>
<h3>shared_array <a name="shared_array_unique">unique</a></h3>
<p><tt>bool unique() const; // never throws</tt></p>
<p><b>T</b> is not required be a complete type.&nbsp;
See <a href="smart_ptr.htm#Common requirements">Common Requirements</a>.</p>
<p>Returns <strong>use_count()</strong> == 1.</p>
<h3><a name="shared_array_swap">shared_array swap</a></h3>
<p><code>void swap( shared_array&lt;T&gt;&amp; other ) throw()</code></p>
<p><b>T</b> is not required be a complete type.&nbsp;
See <a href="smart_ptr.htm#Common requirements">Common Requirements</a>.</p>
<p>Swaps the two smart pointers, as if by std::swap.</p>
<h2>Class <a name="shared_array_example">shared_array example</a></h2>
<p>[To be supplied. In the meantime, see <a href="smart_ptr_test.cpp">smart_ptr_test.cpp</a>.]</p>
<h3><a name="get">get</a></h3>
<pre>T * get() const; // never throws</pre>
<p>Returns the stored pointer.
<b>T</b> need not be a complete type.
See the smart pointer
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
<h3><a name="unique">unique</a></h3>
<pre>bool unique() const; // never throws</pre>
<p>Returns true if no other <b>shared_array</b> is sharing ownership of
the stored pointer, false otherwise.
<b>T</b> need not be a complete type.
See the smart pointer
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
<h3><a name="use_count">use_count</a></h3>
<pre>long use_count() const; // never throws</pre>
<p>Returns the number of <b>shared_array</b> objects sharing ownership of the
stored pointer.
<b>T</b> need not be a complete type.
See the smart pointer
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
<p>Because <b>use_count</b> is not necessarily efficient to implement for
implementations of <b>shared_array</b> that do not use an explicit reference
count, it might be removed from some future version. Thus it should
be used for debugging purposes only, and not production code.</p>
<h3><a name="swap">swap</a></h3>
<pre>void swap(shared_ptr &amp; b); // never throws</pre>
<p>Exchanges the contents of the two smart pointers.
<b>T</b> need not be a complete type.
See the smart pointer
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
<h2><a name="functions">Free Functions</a></h2>
<h3><a name="comparison">comparison</a></h3>
<pre>template&lt;typename T&gt;
bool <a href="#operator==">operator==</a>(shared_array&lt;T&gt; const &amp; a, shared_array&lt;T&gt; const &amp; b); // never throws
template&lt;typename T&gt;
bool <a href="#operator!=">operator!=</a>(shared_array&lt;T&gt; const &amp; a, shared_array&lt;T&gt; const &amp; b); // never throws
template&lt;typename T&gt;
bool <a href="#operator&lt;">operator&lt;</a>(shared_array&lt;T&gt; const &amp; a, shared_array&lt;T&gt; const &amp; b); // never throws</pre>
<p>Compares the stored pointers of the two smart pointers.
<b>T</b> need not be a complete type.
See the smart pointer
<a href="smart_ptr.htm#Common requirements">common requirements</a>.</p>
<p>The <b>operator&lt;</b> overload is provided to define an ordering so that <b>shared_array</b>
objects can be used in associative containers such as <b>std::map</b>.
The implementation uses std::less&lt;T*&gt; to perform the
comparison. This ensures that the comparison is handled correctly, since the
standard mandates that relational operations on pointers are unspecified (5.9 [expr.rel]
paragraph 2) but std::less&lt;&gt; on pointers is well-defined (20.3.3 [lib.comparisons]
paragraph 8).</p>
<h3><a name="free-swap">swap</a></h3>
<pre>template&lt;typename T&gt;
void swap(shared_array&lt;T&gt; &amp; a, shared_array&lt;T&gt; &amp; b) // never throws</pre>
<p>Equivalent to <b>a.swap(b)</b>. Matches the interface of <b>std::swap</b>.
Provided as an aid to generic programming.</p>
<hr>
<p>Revised <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->24 May, 2001<!--webbot bot="Timestamp" endspan i-checksum="13964" -->
</p>
<p>© Copyright Greg Colvin and Beman Dawes 1999. Permission to copy, use,
modify, sell and distribute this document is granted provided this copyright
notice appears in all copies. This document is provided &quot;as is&quot;
without express or implied warranty, and with no claim as to its suitability for
any purpose.</p>
<p>Revised <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B %Y" startspan -->1 February 2002<!--webbot bot="Timestamp" i-checksum="38439" endspan --></p>
<p>Copyright 1999 Greg Colvin and Beman Dawes. Copyright 2002 Darin Adler.
Permission to copy, use, modify, sell and distribute this document is granted
provided this copyright notice appears in all copies.
This document is provided &quot;as is&quot; without express or implied warranty,
and with no claim as to its suitability for any purpose.</p>
</body>