forked from boostorg/type_traits
Add declval and common type from Vicente J. Botet Escriba.
Regenerate docs. [SVN r65443]
This commit is contained in:
John Maddock
219
doc/common_type.qbk
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219
doc/common_type.qbk
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@ -0,0 +1,219 @@
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[/===================================================================]
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[section:common_type common_type]
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[/===================================================================]
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[def __declval [@../../../utility/doc/html/declval.html declval]]
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`#include <boost/type_traits/common_type.hpp>`
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namespace boost {
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template <class ...T> struct __common_type;
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}
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__common_type is a traits class used to deduce a type common to a several types, useful as the return type of functions
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operating on multiple input types such as in mixed-mode arithmetic..
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The nested typedef `::type` could be defined as follows:
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template <class ...T>
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struct common_type;
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template <class T, class U, class ...V>
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struct common_type<T,U,...V> {
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typedef typename __common_type<typename __common_type<T, U>::type, V...>::type type;
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};
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template <class T>
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struct common_type<T> {
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typedef T type;
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};
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template <class T, class U>
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struct common_type<T, U> {
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typedef decltype(__declval<bool>() ? __declval<T>() : __declval<U>()) type;
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};
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All parameter types must be complete. This trait is permitted to be specialized by a user if at least one
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template parameter is a user-defined type. [*Note:] Such specializations are required when only explicit conversions
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are desired among the __common_type arguments.
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Note that when the compiler does not support variadic templates (and the macro BOOST_NO_VARIADIC_TEMPLATES is defined)
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then the maximum number of template arguments is 3.
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[h4 Configuration macros]
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When the compiler does not support static assertions then the user can select the way static assertions are reported. Define
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* BOOST_COMMON_TYPE_USES_STATIC_ASSERT: define it if you want to use Boost.StaticAssert
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* BOOST_COMMON_TYPE_USES_MPL_ASSERT: define it if you want to use Boost.MPL static asertions
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The default behavior is to use mpl assertions in this case, but setting BOOST_COMMON_TYPE_USES_STATIC_ASSERT may reduce
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compile times and header dependencies somewhat.
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Depending on the static assertion used you will have an hint of the failing assertion either through the symbol or through the text.
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When possible common_type is implemented using `decltype`. Otherwise when BOOST_COMMON_TYPE_DONT_USE_TYPEOF is not defined
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it uses Boost.TypeOf.
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[h4 Tutorial]
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In a nutshell, __common_type is a trait that takes 1 or more types, and returns a type which
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all of the types will convert to. The default definition demands this conversion be implicit.
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However the trait can be specialized for user-defined types which want to limit their inter-type conversions to explicit,
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and yet still want to interoperate with the __common_type facility.
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[*Example:]
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template <class T, class U>
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complex<typename __common_type<T, U>::type>
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operator+(complex<T>, complex<U>);
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In the above example, "mixed-mode" complex arithmetic is allowed. The return type is described by __common_type.
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For example the resulting type of adding a `complex<float>` and `complex<double>` might be a `complex<double>`.
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Here is how someone might produce a variadic comparison function:
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template <class ...T>
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typename __common_type<T...>::type
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min(T... t);
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This is a very useful and broadly applicable utility.
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[h4 How to get the common type of types with explicit conversions?]
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Another choice for the author of the preceding operator could be
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template <class T, class U>
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typename __common_type<complex<T>, complex<U> >::type
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operator+(complex<T>, complex<U>);
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As the default definition of __common_type demands the conversion be implicit, we need to specialize the trait for complex types as follows.
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template <class T, class U>
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struct __common_type<complex<T>, complex<U> > {
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typedef complex< __common_type<T, U> > type;
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};
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[h4 How important is the order of the common_type<> template arguments?]
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The order of the template parameters is important.
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`common_type<A,B,C>::type` is not equivalent to `common_type<C,A,B>::type`, but to `common_type<common_type<A,B>::type, C>::type`.
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Consider
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|
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struct A {};
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struct B {};
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struct C {
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C() {}
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C(A const&) {}
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C(B const&) {}
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C& operator=(C const&) {
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return *this;
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}
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};
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The following doesn't compile
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typedef boost::common_type<A, B, C>::type ABC; // Does not compile
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|
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while
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typedef boost::common_type<C, A, B>::type ABC;
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|
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compiles.
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Thus, as `common_type<A,B>::type` is undefined, `common_type<A,B,C>::type` is also undefined.
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It is intended that clients who wish for `common_type<A, B>` to be well
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defined to define it themselves:
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namespace boost
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{
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template <>
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struct common_type<A, B> {typedef C type;};
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}
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Now this client can ask for `common_type<A, B, C>` (and get
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the same answer).
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Clients wanting to ask `common_type<A, B, C>` in any order and get the same result need to add in addition:
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namespace boost
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{
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template <> struct common_type<B, A>
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: public common_type<A, B> {};
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}
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This is needed as the specialization of `common_type<A, B>` is not be used implicitly for `common_type<B, A>`.
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[h4 Can the common_type of two types be a third type?]
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Given the preceding example, one might expect `common_type<A,B>::type` to be `C` without any intervention from the user.
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But the default `common_type<>` implementation doesn't grant that. It is intended that clients who wish for `common_type<A, B>`
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to be well defined to define it themselves:
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namespace boost
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{
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template <>
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struct common_type<A, B> {typedef C type;};
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template <> struct common_type<B, A>
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: public common_type<A, B> {};
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}
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Now this client can ask for `common_type<A, B>`.
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[h4 How common_type behaves with pointers?]
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Consider
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struct C { }:
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struct B : C { };
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struct A : C { };
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Shouldn't `common_type<A*,B*>::type` be `C*`? I would say yes, but the default implementation will make it ill-formed.
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The library could add a specialization for pointers, as
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namespace boost
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{
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template <typename A, typename B>
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struct common_type<A*, B*> {
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typedef common_type<A, B>* type;
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};
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}
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But in the absence of a motivating use cases, we prefer not to add more than the standard specifies.
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Of course the user can always make this specialization.
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[h4 Can you explain the pros/cons of common_type against Boost.Typeof?]
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Even if they appear to be close, `__common_type` and `typeof` have
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different purposes. You use `typeof` to get the type of an expression, while
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you use __common_type to set explicitly the type returned of a template
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function. Both are complementary, and indeed __common_type is equivalent to
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`decltype(__declval<bool>() ? __declval<T>() : __declval<U>())`
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__common_type is also similar to promote_args<class ...T> in boost/math/tools/promotion.hpp,
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though it is not exactly the same as promote_args either. __common_type<T1, T2>::type simply represents the result of some
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operation on T1 and T2, and defaults to the type obtained by putting T1 and T2 into a conditional statement.
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It is meant to be customizable (via specialization) if this default is not appropriate.
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[endsect]
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@ -216,5 +216,22 @@ and enum types to double:
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[endsect]
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[section:improved_min Improving std::min with common_type]
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An improved `std::min` function could be written like this:
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template <class T, class U>
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typename __common_type<T, U>::type min(T t, T u)
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{
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return t < u ? t : u;
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}
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And now expressions such as:
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min(1, 2.0)
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will actually compile and return the correct type!
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[endsect]
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[endsect]
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@ -56,7 +56,7 @@
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method available to them.
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</p>
|
||||
<a name="boost_typetraits.background.type_traits"></a><h5>
|
||||
<a name="id1038712"></a>
|
||||
<a name="id902179"></a>
|
||||
<a class="link" href="background.html#boost_typetraits.background.type_traits">Type Traits</a>
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</h5>
|
||||
<p>
|
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@ -84,7 +84,7 @@
|
||||
given.
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||||
</p>
|
||||
<a name="boost_typetraits.background.implementation"></a><h5>
|
||||
<a name="id1038776"></a>
|
||||
<a name="id902243"></a>
|
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<a class="link" href="background.html#boost_typetraits.background.implementation">Implementation</a>
|
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</h5>
|
||||
<p>
|
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@ -174,7 +174,7 @@
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in the default template.
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</p>
|
||||
<a name="boost_typetraits.background.optimized_copy"></a><h5>
|
||||
<a name="id1039513"></a>
|
||||
<a name="id902979"></a>
|
||||
<a class="link" href="background.html#boost_typetraits.background.optimized_copy">Optimized copy</a>
|
||||
</h5>
|
||||
<p>
|
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@ -247,7 +247,7 @@
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otherwise it will call the "slow but safe version".
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||||
</p>
|
||||
<a name="boost_typetraits.background.was_it_worth_it_"></a><h5>
|
||||
<a name="id1044863"></a>
|
||||
<a name="id908330"></a>
|
||||
<a class="link" href="background.html#boost_typetraits.background.was_it_worth_it_">Was it worth it?</a>
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||||
</h5>
|
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<p>
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@ -280,7 +280,7 @@
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</li>
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||||
</ul></div>
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||||
<div class="table">
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||||
<a name="id1044907"></a><p class="title"><b>Table 1.1. Time taken to copy 1000 elements using `copy<const T*, T*>` (times
|
||||
<a name="id908374"></a><p class="title"><b>Table 1.1. Time taken to copy 1000 elements using `copy<const T*, T*>` (times
|
||||
in micro-seconds)</b></p>
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||||
<div class="table-contents"><table class="table" summary="Time taken to copy 1000 elements using `copy<const T*, T*>` (times
|
||||
in micro-seconds)">
|
||||
@ -379,7 +379,7 @@
|
||||
</table></div>
|
||||
</div>
|
||||
<br class="table-break"><a name="boost_typetraits.background.pair_of_references"></a><h5>
|
||||
<a name="id1045057"></a>
|
||||
<a name="id908524"></a>
|
||||
<a class="link" href="background.html#boost_typetraits.background.pair_of_references">Pair of References</a>
|
||||
</h5>
|
||||
<p>
|
||||
@ -416,7 +416,7 @@
|
||||
to hold non-reference types, references, and constant references:
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1045319"></a><p class="title"><b>Table 1.2. Required Constructor Argument Types</b></p>
|
||||
<a name="id908786"></a><p class="title"><b>Table 1.2. Required Constructor Argument Types</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Required Constructor Argument Types">
|
||||
<colgroup>
|
||||
<col>
|
||||
@ -481,7 +481,7 @@
|
||||
adds a reference to its type, unless it is already a reference.
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1045427"></a><p class="title"><b>Table 1.3. Using add_reference to synthesize the correct constructor type</b></p>
|
||||
<a name="id908894"></a><p class="title"><b>Table 1.3. Using add_reference to synthesize the correct constructor type</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Using add_reference to synthesize the correct constructor type">
|
||||
<colgroup>
|
||||
<col>
|
||||
@ -597,7 +597,7 @@
|
||||
easier to maintain and easier to understand.
|
||||
</p>
|
||||
<a name="boost_typetraits.background.conclusion"></a><h5>
|
||||
<a name="id1045896"></a>
|
||||
<a name="id909363"></a>
|
||||
<a class="link" href="background.html#boost_typetraits.background.conclusion">Conclusion</a>
|
||||
</h5>
|
||||
<p>
|
||||
@ -610,7 +610,7 @@
|
||||
can be optimal as well as generic.
|
||||
</p>
|
||||
<a name="boost_typetraits.background.acknowledgements"></a><h5>
|
||||
<a name="id1045913"></a>
|
||||
<a name="id909380"></a>
|
||||
<a class="link" href="background.html#boost_typetraits.background.acknowledgements">Acknowledgements</a>
|
||||
</h5>
|
||||
<p>
|
||||
@ -618,7 +618,7 @@
|
||||
comments when preparing this article.
|
||||
</p>
|
||||
<a name="background.references"></a><a name="boost_typetraits.background.references"></a><h5>
|
||||
<a name="id1045933"></a>
|
||||
<a name="id909400"></a>
|
||||
<a class="link" href="background.html#boost_typetraits.background.references">References</a>
|
||||
</h5>
|
||||
<div class="orderedlist"><ol type="1">
|
||||
|
||||
@ -57,6 +57,9 @@
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <a class="link" href="../reference/add_volatile.html" title="add_volatile">add_volatile</a><span class="special">;</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <a class="link" href="../reference/common_type.html" title="common_type">common_type</a><span class="special">;</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <a class="link" href="../reference/decay.html" title="decay">decay</a><span class="special">;</span>
|
||||
|
||||
@ -97,7 +100,7 @@
|
||||
<span class="keyword">struct</span> <a class="link" href="../reference/remove_volatile.html" title="remove_volatile">remove_volatile</a><span class="special">;</span>
|
||||
</pre>
|
||||
<a name="boost_typetraits.category.transform.broken_compiler_workarounds_"></a><h5>
|
||||
<a name="id1049903"></a>
|
||||
<a name="id913408"></a>
|
||||
<a class="link" href="transform.html#boost_typetraits.category.transform.broken_compiler_workarounds_">Broken
|
||||
Compiler Workarounds:</a>
|
||||
</h5>
|
||||
|
||||
@ -37,6 +37,8 @@
|
||||
of std::iter_swap</a></span></dt>
|
||||
<dt><span class="section"><a href="examples/to_double.html"> Convert Numeric
|
||||
Types and Enums to double</a></span></dt>
|
||||
<dt><span class="section"><a href="examples/improved_min.html"> Improving std::min
|
||||
with common_type</a></span></dt>
|
||||
</dl></div>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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|
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64
doc/html/boost_typetraits/examples/improved_min.html
Normal file
64
doc/html/boost_typetraits/examples/improved_min.html
Normal file
@ -0,0 +1,64 @@
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<head>
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<div class="section" lang="en">
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<div class="titlepage"><div><div><h3 class="title">
|
||||
<a name="boost_typetraits.examples.improved_min"></a><a class="link" href="improved_min.html" title="Improving std::min with common_type"> Improving std::min
|
||||
with common_type</a>
|
||||
</h3></div></div></div>
|
||||
<p>
|
||||
An improved <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">min</span></code> function could be written like this:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span>
|
||||
<span class="keyword">typename</span> <a class="link" href="../reference/common_type.html" title="common_type">common_type</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">min</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">,</span> <span class="identifier">T</span> <span class="identifier">u</span><span class="special">)</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">return</span> <span class="identifier">t</span> <span class="special"><</span> <span class="identifier">u</span> <span class="special">?</span> <span class="identifier">t</span> <span class="special">:</span> <span class="identifier">u</span><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
And now expressions such as:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">min</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">2.0</span><span class="special">)</span>
|
||||
</pre>
|
||||
<p>
|
||||
will actually compile and return the correct type!
|
||||
</p>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"></td>
|
||||
<td align="right"><div class="copyright-footer">Copyright © 2000, 2006 Adobe Systems Inc, David Abrahams,
|
||||
Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, Jesse Jones, Mat
|
||||
Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert
|
||||
Ramey and Jeremy Siek<p>
|
||||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
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</p>
|
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</div></td>
|
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</tr></table>
|
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<div class="spirit-nav">
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|
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@ -7,7 +7,7 @@
|
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<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits">
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<table cellpadding="2" width="100%"><tr>
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@ -20,7 +20,7 @@
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</tr></table>
|
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<div class="spirit-nav">
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<a accesskey="p" href="iter.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../examples.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../reference.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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</div>
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<div class="section" lang="en">
|
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<div class="titlepage"><div><div><h3 class="title">
|
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@ -52,7 +52,7 @@
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</tr></table>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="iter.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../examples.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../reference.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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<a accesskey="p" href="iter.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../examples.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="improved_min.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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</div>
|
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</body>
|
||||
</html>
|
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|
||||
@ -27,7 +27,7 @@
|
||||
<a name="boost_typetraits.history"></a><a class="link" href="history.html" title="History"> History</a>
|
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</h2></div></div></div>
|
||||
<a name="boost_typetraits.history.boost_1_44_0"></a><h5>
|
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<a name="id1101861"></a>
|
||||
<a name="id969631"></a>
|
||||
<a class="link" href="history.html#boost_typetraits.history.boost_1_44_0">Boost 1.44.0</a>
|
||||
</h5>
|
||||
<div class="itemizedlist"><ul type="disc">
|
||||
@ -43,7 +43,7 @@
|
||||
</li>
|
||||
</ul></div>
|
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<a name="boost_typetraits.history.boost_1_42_0"></a><h5>
|
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<a name="id1101916"></a>
|
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<a name="id969687"></a>
|
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<a class="link" href="history.html#boost_typetraits.history.boost_1_42_0">Boost 1.42.0</a>
|
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</h5>
|
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<div class="itemizedlist"><ul type="disc"><li>
|
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|
||||
@ -99,7 +99,7 @@
|
||||
of the following macros:
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1052050"></a><p class="title"><b>Table 1.4. Macros for Compiler Intrinsics</b></p>
|
||||
<a name="id915555"></a><p class="title"><b>Table 1.4. Macros for Compiler Intrinsics</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Macros for Compiler Intrinsics">
|
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<colgroup>
|
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<col>
|
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@ -6,7 +6,7 @@
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<meta name="generator" content="DocBook XSL Stylesheets V1.74.0">
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<link rel="home" href="../index.html" title="Chapter 1. Boost.TypeTraits">
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<link rel="prev" href="examples/to_double.html" title="Convert Numeric Types and Enums to double">
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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@ -20,7 +20,7 @@
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</tr></table>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="examples/to_double.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="reference/add_const.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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<div class="section" lang="en">
|
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
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@ -36,6 +36,7 @@
|
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<dt><span class="section"><a href="reference/add_volatile.html"> add_volatile</a></span></dt>
|
||||
<dt><span class="section"><a href="reference/aligned_storage.html"> aligned_storage</a></span></dt>
|
||||
<dt><span class="section"><a href="reference/alignment_of.html"> alignment_of</a></span></dt>
|
||||
<dt><span class="section"><a href="reference/common_type.html"> common_type</a></span></dt>
|
||||
<dt><span class="section"><a href="reference/decay.html"> decay</a></span></dt>
|
||||
<dt><span class="section"><a href="reference/extent.html"> extent</a></span></dt>
|
||||
<dt><span class="section"><a href="reference/floating_point_promotion.html">
|
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@ -107,6 +108,8 @@
|
||||
<dt><span class="section"><a href="reference/remove_volatile.html"> remove_volatile</a></span></dt>
|
||||
<dt><span class="section"><a href="reference/type_with_alignment.html"> type_with_alignment</a></span></dt>
|
||||
</dl></div>
|
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<p>
|
||||
</p>
|
||||
</div>
|
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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@ -121,7 +124,7 @@
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</tr></table>
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</div>
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</body>
|
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</html>
|
||||
|
||||
@ -53,7 +53,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1058110"></a><p class="title"><b>Table 1.5. Examples</b></p>
|
||||
<a name="id921834"></a><p class="title"><b>Table 1.5. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -54,7 +54,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1058587"></a><p class="title"><b>Table 1.6. Examples</b></p>
|
||||
<a name="id922312"></a><p class="title"><b>Table 1.6. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
174
doc/html/boost_typetraits/reference/add_lvalue_reference.html
Normal file
174
doc/html/boost_typetraits/reference/add_lvalue_reference.html
Normal file
@ -0,0 +1,174 @@
|
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
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<title>add_lvalue_reference</title>
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<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
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<meta name="generator" content="DocBook XSL Stylesheets V1.74.0">
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<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits">
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<link rel="next" href="add_pointer.html" title="add_pointer">
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<table cellpadding="2" width="100%"><tr>
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<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
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<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
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</div>
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<div class="section" lang="en">
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<div class="titlepage"><div><div><h3 class="title">
|
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<a name="boost_typetraits.reference.add_lvalue_reference"></a><a class="link" href="add_lvalue_reference.html" title="add_lvalue_reference"> add_lvalue_reference</a>
|
||||
</h3></div></div></div>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">add_lvalue_reference</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <em class="replaceable"><code>see-below</code></em> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
</pre>
|
||||
<p>
|
||||
<span class="bold"><strong>type:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
|
||||
names an object or function type then the member typedef <code class="computeroutput"><span class="identifier">type</span></code>
|
||||
shall name <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>;
|
||||
otherwise, if <code class="computeroutput"><span class="identifier">T</span></code> names a type
|
||||
<span class="emphasis"><em>rvalue reference to U</em></span> then the member typedef type shall
|
||||
name <code class="computeroutput"><span class="identifier">U</span><span class="special">&</span></code>;
|
||||
otherwise, type shall name <code class="computeroutput"><span class="identifier">T</span></code>.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>C++ Standard Reference:</strong></span> 20.7.6.2.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>Compiler Compatibility:</strong></span> If the compiler
|
||||
does not support partial specialization of class-templates then this template
|
||||
will compile, but the member <code class="computeroutput"><span class="identifier">type</span></code>
|
||||
will always be the same as type <code class="computeroutput"><span class="identifier">T</span></code>
|
||||
except where <a class="link" href="../category/transform.html#boost_typetraits.category.transform.broken_compiler_workarounds_">compiler
|
||||
workarounds</a> have been applied.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
|
||||
<span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">add_lvalue_reference</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id922834"></a><p class="title"><b>Table 1.7. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
<col>
|
||||
</colgroup>
|
||||
<thead><tr>
|
||||
<th>
|
||||
<p>
|
||||
Expression
|
||||
</p>
|
||||
</th>
|
||||
<th>
|
||||
<p>
|
||||
Result Type
|
||||
</p>
|
||||
</th>
|
||||
</tr></thead>
|
||||
<tbody>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_lvalue_reference</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span><span class="special">&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_lvalue_reference</span><span class="special"><</span><span class="keyword">int</span>
|
||||
<span class="keyword">const</span><span class="special">&>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span> <span class="keyword">const</span><span class="special">&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_lvalue_reference</span><span class="special"><</span><span class="keyword">int</span><span class="special">*>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span><span class="special">*&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_lvalue_reference</span><span class="special"><</span><span class="keyword">int</span><span class="special">*&>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span><span class="special">*&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_lvalue_reference</span><span class="special"><</span><span class="keyword">int</span><span class="special">&&>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span><span class="special">&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_lvalue_reference</span><span class="special"><</span><span class="keyword">void</span><span class="special">>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">void</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
</tbody>
|
||||
</table></div>
|
||||
</div>
|
||||
<br class="table-break">
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"></td>
|
||||
<td align="right"><div class="copyright-footer">Copyright © 2000, 2006 Adobe Systems Inc, David Abrahams,
|
||||
Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, Jesse Jones, Mat
|
||||
Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert
|
||||
Ramey and Jeremy Siek<p>
|
||||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||||
</p>
|
||||
</div></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="add_cv.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="add_pointer.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
@ -56,7 +56,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1059719"></a><p class="title"><b>Table 1.8. Examples</b></p>
|
||||
<a name="id923444"></a><p class="title"><b>Table 1.8. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -65,7 +65,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1060217"></a><p class="title"><b>Table 1.9. Examples</b></p>
|
||||
<a name="id923942"></a><p class="title"><b>Table 1.9. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
172
doc/html/boost_typetraits/reference/add_rvalue_reference.html
Normal file
172
doc/html/boost_typetraits/reference/add_rvalue_reference.html
Normal file
@ -0,0 +1,172 @@
|
||||
<html>
|
||||
<head>
|
||||
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
|
||||
<title>add_rvalue_reference</title>
|
||||
<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
|
||||
<meta name="generator" content="DocBook XSL Stylesheets V1.74.0">
|
||||
<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits">
|
||||
<link rel="up" href="../reference.html" title="Alphabetical Reference">
|
||||
<link rel="prev" href="add_reference.html" title="add_reference">
|
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<link rel="next" href="add_volatile.html" title="add_volatile">
|
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|
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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||||
<table cellpadding="2" width="100%"><tr>
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||||
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
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||||
<td align="center"><a href="../../../../../../index.html">Home</a></td>
|
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<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
|
||||
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
|
||||
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
|
||||
<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="add_reference.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="add_volatile.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
<a name="boost_typetraits.reference.add_rvalue_reference"></a><a class="link" href="add_rvalue_reference.html" title="add_rvalue_reference"> add_rvalue_reference</a>
|
||||
</h3></div></div></div>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">add_rvalue_reference</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <em class="replaceable"><code>see-below</code></em> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
</pre>
|
||||
<p>
|
||||
<span class="bold"><strong>type:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
|
||||
names an object or function type then the member typedef type shall name
|
||||
<code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span></code>;
|
||||
otherwise, type shall name <code class="computeroutput"><span class="identifier">T</span></code>.
|
||||
<span class="emphasis"><em>[Note: This rule reflects the semantics of reference collapsing.
|
||||
For example, when a type <code class="computeroutput"><span class="identifier">T</span></code>
|
||||
names a type U&, the type <code class="computeroutput"><span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span></code> is not an rvalue reference. -end note]</em></span>.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>C++ Standard Reference:</strong></span> 20.7.6.2.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>Compiler Compatibility:</strong></span> If the compiler
|
||||
does not support partial specialization of class-templates and rvalue references
|
||||
then this template will compile, but the member <code class="computeroutput"><span class="identifier">type</span></code>
|
||||
will always be the same as type <code class="computeroutput"><span class="identifier">T</span></code>.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
|
||||
<span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">add_rvalue_reference</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id924446"></a><p class="title"><b>Table 1.10. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
<col>
|
||||
</colgroup>
|
||||
<thead><tr>
|
||||
<th>
|
||||
<p>
|
||||
Expression
|
||||
</p>
|
||||
</th>
|
||||
<th>
|
||||
<p>
|
||||
Result Type
|
||||
</p>
|
||||
</th>
|
||||
</tr></thead>
|
||||
<tbody>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span><span class="special">&&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="keyword">int</span>
|
||||
<span class="keyword">const</span><span class="special">&>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span> <span class="keyword">const</span><span class="special">&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="keyword">int</span><span class="special">*>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span><span class="special">*&&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="keyword">int</span><span class="special">*&>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span><span class="special">*&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="keyword">int</span><span class="special">&&>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">int</span><span class="special">&&</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="keyword">void</span><span class="special">>::</span><span class="identifier">type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="keyword">void</span></code>
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
</tbody>
|
||||
</table></div>
|
||||
</div>
|
||||
<br class="table-break">
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"></td>
|
||||
<td align="right"><div class="copyright-footer">Copyright © 2000, 2006 Adobe Systems Inc, David Abrahams,
|
||||
Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, Jesse Jones, Mat
|
||||
Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert
|
||||
Ramey and Jeremy Siek<p>
|
||||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||||
</p>
|
||||
</div></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="add_reference.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="add_volatile.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
@ -53,7 +53,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1061289"></a><p class="title"><b>Table 1.11. Examples</b></p>
|
||||
<a name="id925014"></a><p class="title"><b>Table 1.11. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -7,7 +7,7 @@
|
||||
<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits">
|
||||
<link rel="up" href="../reference.html" title="Alphabetical Reference">
|
||||
<link rel="prev" href="aligned_storage.html" title="aligned_storage">
|
||||
<link rel="next" href="decay.html" title="decay">
|
||||
<link rel="next" href="common_type.html" title="common_type">
|
||||
</head>
|
||||
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
|
||||
<table cellpadding="2" width="100%"><tr>
|
||||
@ -20,7 +20,7 @@
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="aligned_storage.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="decay.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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<a accesskey="p" href="aligned_storage.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="common_type.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
@ -76,7 +76,7 @@
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="aligned_storage.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="decay.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
|
||||
350
doc/html/boost_typetraits/reference/common_type.html
Normal file
350
doc/html/boost_typetraits/reference/common_type.html
Normal file
@ -0,0 +1,350 @@
|
||||
<html>
|
||||
<head>
|
||||
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
|
||||
<title>common_type</title>
|
||||
<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
|
||||
<meta name="generator" content="DocBook XSL Stylesheets V1.74.0">
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<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits">
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<link rel="up" href="../reference.html" title="Alphabetical Reference">
|
||||
<link rel="prev" href="alignment_of.html" title="alignment_of">
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<link rel="next" href="decay.html" title="decay">
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<table cellpadding="2" width="100%"><tr>
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<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
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<td align="center"><a href="../../../../../../index.html">Home</a></td>
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<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
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<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
|
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<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
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<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
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|
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<a accesskey="p" href="alignment_of.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="decay.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
<a name="boost_typetraits.reference.common_type"></a><a class="link" href="common_type.html" title="common_type"> common_type</a>
|
||||
</h3></div></div></div>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">common_type</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="special">...</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">struct</span> <a class="link" href="common_type.html" title="common_type">common_type</a><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
<a class="link" href="common_type.html" title="common_type">common_type</a>
|
||||
is a traits class used to deduce a type common to a several types, useful
|
||||
as the return type of functions operating on multiple input types such as
|
||||
in mixed-mode arithmetic..
|
||||
</p>
|
||||
<p>
|
||||
The nested typedef <code class="computeroutput"><span class="special">::</span><span class="identifier">type</span></code>
|
||||
could be defined as follows:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="special">...</span><span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special">;</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">,</span> <span class="keyword">class</span> <span class="special">...</span><span class="identifier">V</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">U</span><span class="special">,...</span><span class="identifier">V</span><span class="special">></span> <span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <span class="keyword">typename</span> <a class="link" href="common_type.html" title="common_type">common_type</a><span class="special"><</span><span class="keyword">typename</span> <a class="link" href="common_type.html" title="common_type">common_type</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">V</span><span class="special">...>::</span><span class="identifier">type</span> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <span class="identifier">T</span> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">></span> <span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <span class="identifier">decltype</span><span class="special">(</span><a href="../../../../../utility/doc/html/declval.html" target="_top">declval</a><span class="special"><</span><span class="keyword">bool</span><span class="special">>()</span> <span class="special">?</span> <a href="../../../../../utility/doc/html/declval.html" target="_top">declval</a><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span> <span class="special">:</span> <a href="../../../../../utility/doc/html/declval.html" target="_top">declval</a><span class="special"><</span><span class="identifier">U</span><span class="special">>())</span> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
</pre>
|
||||
<p>
|
||||
All parameter types must be complete. This trait is permitted to be specialized
|
||||
by a user if at least one template parameter is a user-defined type. <span class="bold"><strong>Note:</strong></span> Such specializations are required when only
|
||||
explicit conversions are desired among the <a class="link" href="common_type.html" title="common_type">common_type</a>
|
||||
arguments.
|
||||
</p>
|
||||
<p>
|
||||
Note that when the compiler does not support variadic templates (and the
|
||||
macro BOOST_NO_VARIADIC_TEMPLATES is defined) then the maximum number of
|
||||
template arguments is 3.
|
||||
</p>
|
||||
<a name="boost_typetraits.reference.common_type.configuration_macros"></a><h5>
|
||||
<a name="id928233"></a>
|
||||
<a class="link" href="common_type.html#boost_typetraits.reference.common_type.configuration_macros">Configuration
|
||||
macros</a>
|
||||
</h5>
|
||||
<p>
|
||||
When the compiler does not support static assertions then the user can select
|
||||
the way static assertions are reported. Define
|
||||
</p>
|
||||
<div class="itemizedlist"><ul type="disc">
|
||||
<li>
|
||||
BOOST_COMMON_TYPE_USES_STATIC_ASSERT: define it if you want to use Boost.StaticAssert
|
||||
</li>
|
||||
<li>
|
||||
BOOST_COMMON_TYPE_USES_MPL_ASSERT: define it if you want to use Boost.MPL
|
||||
static asertions
|
||||
</li>
|
||||
</ul></div>
|
||||
<p>
|
||||
The default behavior is to use mpl assertions in this case, but setting BOOST_COMMON_TYPE_USES_STATIC_ASSERT
|
||||
may reduce compile times and header dependencies somewhat.
|
||||
</p>
|
||||
<p>
|
||||
Depending on the static assertion used you will have an hint of the failing
|
||||
assertion either through the symbol or through the text.
|
||||
</p>
|
||||
<p>
|
||||
When possible common_type is implemented using <code class="computeroutput"><span class="identifier">decltype</span></code>.
|
||||
Otherwise when BOOST_COMMON_TYPE_DONT_USE_TYPEOF is not defined it uses Boost.TypeOf.
|
||||
</p>
|
||||
<a name="boost_typetraits.reference.common_type.tutorial"></a><h5>
|
||||
<a name="id928289"></a>
|
||||
<a class="link" href="common_type.html#boost_typetraits.reference.common_type.tutorial">Tutorial</a>
|
||||
</h5>
|
||||
<p>
|
||||
In a nutshell, <a class="link" href="common_type.html" title="common_type">common_type</a>
|
||||
is a trait that takes 1 or more types, and returns a type which all of the
|
||||
types will convert to. The default definition demands this conversion be
|
||||
implicit. However the trait can be specialized for user-defined types which
|
||||
want to limit their inter-type conversions to explicit, and yet still want
|
||||
to interoperate with the <a class="link" href="common_type.html" title="common_type">common_type</a>
|
||||
facility.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>Example:</strong></span>
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span>
|
||||
<span class="identifier">complex</span><span class="special"><</span><span class="keyword">typename</span> <a class="link" href="common_type.html" title="common_type">common_type</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">>::</span><span class="identifier">type</span><span class="special">></span>
|
||||
<span class="keyword">operator</span><span class="special">+(</span><span class="identifier">complex</span><span class="special"><</span><span class="identifier">T</span><span class="special">>,</span> <span class="identifier">complex</span><span class="special"><</span><span class="identifier">U</span><span class="special">>);</span>
|
||||
</pre>
|
||||
<p>
|
||||
In the above example, "mixed-mode" complex arithmetic is allowed.
|
||||
The return type is described by <a class="link" href="common_type.html" title="common_type">common_type</a>.
|
||||
For example the resulting type of adding a <code class="computeroutput"><span class="identifier">complex</span><span class="special"><</span><span class="keyword">float</span><span class="special">></span></code> and <code class="computeroutput"><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span></code> might be a <code class="computeroutput"><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span></code>.
|
||||
</p>
|
||||
<p>
|
||||
Here is how someone might produce a variadic comparison function:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="special">...</span><span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">typename</span> <a class="link" href="common_type.html" title="common_type">common_type</a><span class="special"><</span><span class="identifier">T</span><span class="special">...>::</span><span class="identifier">type</span>
|
||||
<span class="identifier">min</span><span class="special">(</span><span class="identifier">T</span><span class="special">...</span> <span class="identifier">t</span><span class="special">);</span>
|
||||
</pre>
|
||||
<p>
|
||||
This is a very useful and broadly applicable utility.
|
||||
</p>
|
||||
<a name="boost_typetraits.reference.common_type.how_to_get_the_common_type_of_types_with_explicit_conversions_"></a><h5>
|
||||
<a name="id928590"></a>
|
||||
<a class="link" href="common_type.html#boost_typetraits.reference.common_type.how_to_get_the_common_type_of_types_with_explicit_conversions_">How
|
||||
to get the common type of types with explicit conversions?</a>
|
||||
</h5>
|
||||
<p>
|
||||
Another choice for the author of the preceding operator could be
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span>
|
||||
<span class="keyword">typename</span> <a class="link" href="common_type.html" title="common_type">common_type</a><span class="special"><</span><span class="identifier">complex</span><span class="special"><</span><span class="identifier">T</span><span class="special">>,</span> <span class="identifier">complex</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="special">>::</span><span class="identifier">type</span>
|
||||
<span class="keyword">operator</span><span class="special">+(</span><span class="identifier">complex</span><span class="special"><</span><span class="identifier">T</span><span class="special">>,</span> <span class="identifier">complex</span><span class="special"><</span><span class="identifier">U</span><span class="special">>);</span>
|
||||
</pre>
|
||||
<p>
|
||||
As the default definition of <a class="link" href="common_type.html" title="common_type">common_type</a>
|
||||
demands the conversion be implicit, we need to specialize the trait for complex
|
||||
types as follows.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <a class="link" href="common_type.html" title="common_type">common_type</a><span class="special"><</span><span class="identifier">complex</span><span class="special"><</span><span class="identifier">T</span><span class="special">>,</span> <span class="identifier">complex</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="special">></span> <span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <span class="identifier">complex</span><span class="special"><</span> <a class="link" href="common_type.html" title="common_type">common_type</a><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">></span> <span class="special">></span> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
</pre>
|
||||
<a name="boost_typetraits.reference.common_type.how_important_is_the_order_of_the_common_type_lt__gt__template_arguments_"></a><h5>
|
||||
<a name="id928890"></a>
|
||||
<a class="link" href="common_type.html#boost_typetraits.reference.common_type.how_important_is_the_order_of_the_common_type_lt__gt__template_arguments_">How
|
||||
important is the order of the common_type<> template arguments?</a>
|
||||
</h5>
|
||||
<p>
|
||||
The order of the template parameters is important.
|
||||
</p>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span><span class="identifier">B</span><span class="special">,</span><span class="identifier">C</span><span class="special">>::</span><span class="identifier">type</span></code> is not equivalent to <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">C</span><span class="special">,</span><span class="identifier">A</span><span class="special">,</span><span class="identifier">B</span><span class="special">>::</span><span class="identifier">type</span></code>, but to <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span><span class="identifier">B</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">C</span><span class="special">>::</span><span class="identifier">type</span></code>.
|
||||
</p>
|
||||
<p>
|
||||
Consider
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">A</span> <span class="special">{};</span>
|
||||
<span class="keyword">struct</span> <span class="identifier">B</span> <span class="special">{};</span>
|
||||
<span class="keyword">struct</span> <span class="identifier">C</span> <span class="special">{</span>
|
||||
<span class="identifier">C</span><span class="special">()</span> <span class="special">{}</span>
|
||||
<span class="identifier">C</span><span class="special">(</span><span class="identifier">A</span> <span class="keyword">const</span><span class="special">&)</span> <span class="special">{}</span>
|
||||
<span class="identifier">C</span><span class="special">(</span><span class="identifier">B</span> <span class="keyword">const</span><span class="special">&)</span> <span class="special">{}</span>
|
||||
<span class="identifier">C</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">C</span> <span class="keyword">const</span><span class="special">&)</span> <span class="special">{</span>
|
||||
<span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
<span class="special">};</span>
|
||||
</pre>
|
||||
<p>
|
||||
The following doesn't compile
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">,</span> <span class="identifier">C</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">ABC</span><span class="special">;</span> <span class="comment">// Does not compile
|
||||
</span></pre>
|
||||
<p>
|
||||
while
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">C</span><span class="special">,</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">ABC</span><span class="special">;</span>
|
||||
</pre>
|
||||
<p>
|
||||
compiles.
|
||||
</p>
|
||||
<p>
|
||||
Thus, as <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span><span class="identifier">B</span><span class="special">>::</span><span class="identifier">type</span></code>
|
||||
is undefined, <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span><span class="identifier">B</span><span class="special">,</span><span class="identifier">C</span><span class="special">>::</span><span class="identifier">type</span></code>
|
||||
is also undefined.
|
||||
</p>
|
||||
<p>
|
||||
It is intended that clients who wish for <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span>
|
||||
<span class="identifier">B</span><span class="special">></span></code>
|
||||
to be well defined to define it themselves:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
|
||||
<span class="special">{</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">></span> <span class="special">{</span><span class="keyword">typedef</span> <span class="identifier">C</span> <span class="identifier">type</span><span class="special">;};</span>
|
||||
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
Now this client can ask for <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span>
|
||||
<span class="identifier">B</span><span class="special">,</span> <span class="identifier">C</span><span class="special">></span></code> (and
|
||||
get the same answer).
|
||||
</p>
|
||||
<p>
|
||||
Clients wanting to ask <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span>
|
||||
<span class="identifier">B</span><span class="special">,</span> <span class="identifier">C</span><span class="special">></span></code> in
|
||||
any order and get the same result need to add in addition:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
|
||||
<span class="special">{</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><></span> <span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">B</span><span class="special">,</span> <span class="identifier">A</span><span class="special">></span>
|
||||
<span class="special">:</span> <span class="keyword">public</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">></span> <span class="special">{};</span>
|
||||
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
This is needed as the specialization of <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span>
|
||||
<span class="identifier">B</span><span class="special">></span></code>
|
||||
is not be used implicitly for <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">B</span><span class="special">,</span>
|
||||
<span class="identifier">A</span><span class="special">></span></code>.
|
||||
</p>
|
||||
<a name="boost_typetraits.reference.common_type.can_the_common_type_of_two_types_be_a_third_type_"></a><h5>
|
||||
<a name="id929759"></a>
|
||||
<a class="link" href="common_type.html#boost_typetraits.reference.common_type.can_the_common_type_of_two_types_be_a_third_type_">Can
|
||||
the common_type of two types be a third type?</a>
|
||||
</h5>
|
||||
<p>
|
||||
Given the preceding example, one might expect <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span><span class="identifier">B</span><span class="special">>::</span><span class="identifier">type</span></code> to be <code class="computeroutput"><span class="identifier">C</span></code>
|
||||
without any intervention from the user. But the default <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><></span></code> implementation doesn't grant that.
|
||||
It is intended that clients who wish for <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span>
|
||||
<span class="identifier">B</span><span class="special">></span></code>
|
||||
to be well defined to define it themselves:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
|
||||
<span class="special">{</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">></span> <span class="special">{</span><span class="keyword">typedef</span> <span class="identifier">C</span> <span class="identifier">type</span><span class="special">;};</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><></span> <span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">B</span><span class="special">,</span> <span class="identifier">A</span><span class="special">></span>
|
||||
<span class="special">:</span> <span class="keyword">public</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">></span> <span class="special">{};</span>
|
||||
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
Now this client can ask for <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span>
|
||||
<span class="identifier">B</span><span class="special">></span></code>.
|
||||
</p>
|
||||
<a name="boost_typetraits.reference.common_type.how_common_type_behaves_with_pointers_"></a><h5>
|
||||
<a name="id930041"></a>
|
||||
<a class="link" href="common_type.html#boost_typetraits.reference.common_type.how_common_type_behaves_with_pointers_">How
|
||||
common_type behaves with pointers?</a>
|
||||
</h5>
|
||||
<p>
|
||||
Consider
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">C</span> <span class="special">{</span> <span class="special">}:</span>
|
||||
<span class="keyword">struct</span> <span class="identifier">B</span> <span class="special">:</span> <span class="identifier">C</span> <span class="special">{</span> <span class="special">};</span>
|
||||
<span class="keyword">struct</span> <span class="identifier">A</span> <span class="special">:</span> <span class="identifier">C</span> <span class="special">{</span> <span class="special">};</span>
|
||||
</pre>
|
||||
<p>
|
||||
Shouldn't <code class="computeroutput"><span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">*,</span><span class="identifier">B</span><span class="special">*>::</span><span class="identifier">type</span></code>
|
||||
be <code class="computeroutput"><span class="identifier">C</span><span class="special">*</span></code>?
|
||||
I would say yes, but the default implementation will make it ill-formed.
|
||||
</p>
|
||||
<p>
|
||||
The library could add a specialization for pointers, as
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
|
||||
<span class="special">{</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">B</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">*,</span> <span class="identifier">B</span><span class="special">*></span> <span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">>*</span> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
But in the absence of a motivating use cases, we prefer not to add more than
|
||||
the standard specifies.
|
||||
</p>
|
||||
<p>
|
||||
Of course the user can always make this specialization.
|
||||
</p>
|
||||
<a name="boost_typetraits.reference.common_type.can_you_explain_the_pros_cons_of_common_type_against_boost_typeof_"></a><h5>
|
||||
<a name="id930325"></a>
|
||||
<a class="link" href="common_type.html#boost_typetraits.reference.common_type.can_you_explain_the_pros_cons_of_common_type_against_boost_typeof_">Can
|
||||
you explain the pros/cons of common_type against Boost.Typeof?</a>
|
||||
</h5>
|
||||
<p>
|
||||
Even if they appear to be close, <code class="computeroutput"><a class="link" href="common_type.html" title="common_type">common_type</a></code>
|
||||
and <code class="computeroutput"><span class="identifier">typeof</span></code> have different
|
||||
purposes. You use <code class="computeroutput"><span class="identifier">typeof</span></code>
|
||||
to get the type of an expression, while you use <a class="link" href="common_type.html" title="common_type">common_type</a>
|
||||
to set explicitly the type returned of a template function. Both are complementary,
|
||||
and indeed <a class="link" href="common_type.html" title="common_type">common_type</a>
|
||||
is equivalent to <code class="computeroutput"><span class="identifier">decltype</span><span class="special">(</span><a href="../../../../../utility/doc/html/declval.html" target="_top">declval</a><span class="special"><</span><span class="keyword">bool</span><span class="special">>()</span>
|
||||
<span class="special">?</span> <a href="../../../../../utility/doc/html/declval.html" target="_top">declval</a><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span>
|
||||
<span class="special">:</span> <a href="../../../../../utility/doc/html/declval.html" target="_top">declval</a><span class="special"><</span><span class="identifier">U</span><span class="special">>())</span></code>
|
||||
</p>
|
||||
<p>
|
||||
<a class="link" href="common_type.html" title="common_type">common_type</a>
|
||||
is also similar to promote_args<class ...T> in boost/math/tools/promotion.hpp,
|
||||
though it is not exactly the same as promote_args either. <a class="link" href="common_type.html" title="common_type">common_type</a><T1,
|
||||
T2>::type simply represents the result of some operation on T1 and T2,
|
||||
and defaults to the type obtained by putting T1 and T2 into a conditional
|
||||
statement.
|
||||
</p>
|
||||
<p>
|
||||
It is meant to be customizable (via specialization) if this default is not
|
||||
appropriate.
|
||||
</p>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"></td>
|
||||
<td align="right"><div class="copyright-footer">Copyright © 2000, 2006 Adobe Systems Inc, David Abrahams,
|
||||
Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, Jesse Jones, Mat
|
||||
Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert
|
||||
Ramey and Jeremy Siek<p>
|
||||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||||
</p>
|
||||
</div></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="alignment_of.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="decay.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
117
doc/html/boost_typetraits/reference/common_type_hpp.html
Normal file
117
doc/html/boost_typetraits/reference/common_type_hpp.html
Normal file
@ -0,0 +1,117 @@
|
||||
<html>
|
||||
<head>
|
||||
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
|
||||
<title>common_type</title>
|
||||
<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
|
||||
<meta name="generator" content="DocBook XSL Stylesheets V1.74.0">
|
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<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits">
|
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<link rel="up" href="../reference.html" title="Alphabetical Reference">
|
||||
<link rel="prev" href="alignment_of.html" title="alignment_of">
|
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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<table cellpadding="2" width="100%"><tr>
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<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
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|
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<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
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<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
|
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|
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<a accesskey="p" href="alignment_of.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="decay.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
<a name="boost_typetraits.reference.common_type_hpp"></a><a class="link" href="common_type_hpp.html" title="common_type"> common_type</a>
|
||||
</h3></div></div></div>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">common_type</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="special">...</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">struct</span> <a class="link" href="../../">common_type</a><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
<a class="link" href="../../">common_type</a>
|
||||
is a traits class used to deduce a type common to a several types, useful
|
||||
as the return type of functions operating on multiple input types such as
|
||||
in mixed-mode arithmetic..
|
||||
</p>
|
||||
<p>
|
||||
The nested typedef <code class="computeroutput"><span class="special">::</span><span class="identifier">type</span></code>
|
||||
could be defined as follows:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="special">...</span><span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special">;</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">,</span> <span class="keyword">class</span> <span class="special">...</span><span class="identifier">V</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">U</span><span class="special">,...</span><span class="identifier">V</span><span class="special">></span> <span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">__common_type__</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">__common_type__</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">V</span><span class="special">...>::</span><span class="identifier">type</span> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <span class="identifier">T</span> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">common_type</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">></span> <span class="special">{</span>
|
||||
<span class="keyword">typedef</span> <span class="identifier">decltype</span><span class="special">(</span><span class="identifier">__declval__</span><span class="special"><</span><span class="keyword">bool</span><span class="special">>()</span> <span class="special">?</span> <span class="identifier">__declval__</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span> <span class="special">:</span> <span class="identifier">__declval__</span><span class="special"><</span><span class="identifier">U</span><span class="special">>())</span> <span class="identifier">type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
</pre>
|
||||
<p>
|
||||
All parameter types must be complete. This trait is permitted to be specialized
|
||||
by a user if at least one template parameter is a user-defined type. <span class="bold"><strong>Note:</strong></span> Such specializations are required when only
|
||||
explicit conversions are desired among the <a class="link" href="../../">common_type</a>
|
||||
arguments.
|
||||
</p>
|
||||
<a name="boost_typetraits.reference.common_type_hpp.configuration_macros"></a><h5>
|
||||
<a name="id895242"></a>
|
||||
<a class="link" href="common_type_hpp.html#boost_typetraits.reference.common_type_hpp.configuration_macros">Configuration
|
||||
macros</a>
|
||||
</h5>
|
||||
<p>
|
||||
When the compiler does not support static assertions then the user can select
|
||||
the way static assertions are reported. Define
|
||||
</p>
|
||||
<div class="itemizedlist"><ul type="disc">
|
||||
<li>
|
||||
BOOST_COMMON_TYPE_USES_STATIC_ASSERT: define it if you want to use Boost.StaticAssert
|
||||
</li>
|
||||
<li>
|
||||
BOOST_COMMON_TYPE_USES_MPL_ASSERT: define it if you want to use Boost.MPL
|
||||
static asertions
|
||||
</li>
|
||||
</ul></div>
|
||||
<p>
|
||||
The default behavior is to use mpl assertions in this case, but setting BOOST_COMMON_TYPE_USES_STATIC_ASSERT
|
||||
may reduce compile times and header dependencies somewhat.
|
||||
</p>
|
||||
<p>
|
||||
Depending on the static assertion used you will have an hint of the failing
|
||||
assertion either through the symbol or through the text.
|
||||
</p>
|
||||
<p>
|
||||
When possible common_type is implemented using <code class="computeroutput"><span class="identifier">decltype</span></code>.
|
||||
Otherwise when BOOST_COMMON_TYPE_DONT_USE_TYPEOF is not defined it uses Boost.TypeOf.
|
||||
</p>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"></td>
|
||||
<td align="right"><div class="copyright-footer">Copyright © 2000, 2006 Adobe Systems Inc, David Abrahams,
|
||||
Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, Jesse Jones, Mat
|
||||
Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert
|
||||
Ramey and Jeremy Siek<p>
|
||||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||||
</p>
|
||||
</div></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="alignment_of.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="decay.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
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</div>
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</body>
|
||||
</html>
|
||||
@ -6,7 +6,7 @@
|
||||
<meta name="generator" content="DocBook XSL Stylesheets V1.74.0">
|
||||
<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits">
|
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<link rel="up" href="../reference.html" title="Alphabetical Reference">
|
||||
<link rel="prev" href="alignment_of.html" title="alignment_of">
|
||||
<link rel="prev" href="common_type.html" title="common_type">
|
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<link rel="next" href="extent.html" title="extent">
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</head>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
|
||||
@ -20,7 +20,7 @@
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="alignment_of.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="extent.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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<a accesskey="p" href="common_type.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="extent.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
@ -48,7 +48,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1064172"></a><p class="title"><b>Table 1.12. Examples</b></p>
|
||||
<a name="id930714"></a><p class="title"><b>Table 1.12. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
@ -145,7 +145,7 @@
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav">
|
||||
<a accesskey="p" href="alignment_of.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="extent.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
<a accesskey="p" href="common_type.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="extent.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
|
||||
@ -49,7 +49,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1065724"></a><p class="title"><b>Table 1.13. Examples</b></p>
|
||||
<a name="id933358"></a><p class="title"><b>Table 1.13. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -59,7 +59,7 @@
|
||||
</p></td></tr>
|
||||
</table></div>
|
||||
<div class="table">
|
||||
<a name="id1066098"></a><p class="title"><b>Table 1.14. Function Traits Members</b></p>
|
||||
<a name="id933731"></a><p class="title"><b>Table 1.14. Function Traits Members</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Function Traits Members">
|
||||
<colgroup>
|
||||
<col>
|
||||
@ -122,7 +122,7 @@
|
||||
</table></div>
|
||||
</div>
|
||||
<br class="table-break"><div class="table">
|
||||
<a name="id1066315"></a><p class="title"><b>Table 1.15. Examples</b></p>
|
||||
<a name="id933949"></a><p class="title"><b>Table 1.15. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -49,7 +49,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1071961"></a><p class="title"><b>Table 1.16. Examples</b></p>
|
||||
<a name="id940687"></a><p class="title"><b>Table 1.16. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -54,7 +54,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1093886"></a><p class="title"><b>Table 1.17. Examples</b></p>
|
||||
<a name="id961588"></a><p class="title"><b>Table 1.17. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -54,7 +54,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1094368"></a><p class="title"><b>Table 1.18. Examples</b></p>
|
||||
<a name="id962071"></a><p class="title"><b>Table 1.18. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -51,7 +51,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1094893"></a><p class="title"><b>Table 1.19. Examples</b></p>
|
||||
<a name="id963756"></a><p class="title"><b>Table 1.19. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -54,7 +54,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1097629"></a><p class="title"><b>Table 1.20. Examples</b></p>
|
||||
<a name="id964853"></a><p class="title"><b>Table 1.20. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -53,7 +53,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1098172"></a><p class="title"><b>Table 1.21. Examples</b></p>
|
||||
<a name="id965396"></a><p class="title"><b>Table 1.21. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -53,7 +53,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1098703"></a><p class="title"><b>Table 1.22. Examples</b></p>
|
||||
<a name="id967020"></a><p class="title"><b>Table 1.22. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -54,7 +54,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1099232"></a><p class="title"><b>Table 1.23. Examples</b></p>
|
||||
<a name="id967549"></a><p class="title"><b>Table 1.23. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -55,7 +55,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1099787"></a><p class="title"><b>Table 1.24. Examples</b></p>
|
||||
<a name="id968103"></a><p class="title"><b>Table 1.24. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -53,7 +53,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1100299"></a><p class="title"><b>Table 1.25. Examples</b></p>
|
||||
<a name="id968616"></a><p class="title"><b>Table 1.25. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -53,7 +53,7 @@
|
||||
or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<div class="table">
|
||||
<a name="id1100801"></a><p class="title"><b>Table 1.26. Examples</b></p>
|
||||
<a name="id969118"></a><p class="title"><b>Table 1.26. Examples</b></p>
|
||||
<div class="table-contents"><table class="table" summary="Examples">
|
||||
<colgroup>
|
||||
<col>
|
||||
|
||||
@ -30,7 +30,7 @@
|
||||
Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert
|
||||
Ramey and Jeremy Siek</p></div>
|
||||
<div><div class="legalnotice">
|
||||
<a name="id1038564"></a><p>
|
||||
<a name="id902030"></a><p>
|
||||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||||
</p>
|
||||
@ -75,6 +75,8 @@
|
||||
of std::iter_swap</a></span></dt>
|
||||
<dt><span class="section"><a href="boost_typetraits/examples/to_double.html"> Convert Numeric
|
||||
Types and Enums to double</a></span></dt>
|
||||
<dt><span class="section"><a href="boost_typetraits/examples/improved_min.html"> Improving std::min
|
||||
with common_type</a></span></dt>
|
||||
</dl></dd>
|
||||
<dt><span class="section"><a href="boost_typetraits/reference.html"> Alphabetical Reference</a></span></dt>
|
||||
<dd><dl>
|
||||
@ -87,6 +89,7 @@
|
||||
<dt><span class="section"><a href="boost_typetraits/reference/add_volatile.html"> add_volatile</a></span></dt>
|
||||
<dt><span class="section"><a href="boost_typetraits/reference/aligned_storage.html"> aligned_storage</a></span></dt>
|
||||
<dt><span class="section"><a href="boost_typetraits/reference/alignment_of.html"> alignment_of</a></span></dt>
|
||||
<dt><span class="section"><a href="boost_typetraits/reference/common_type.html"> common_type</a></span></dt>
|
||||
<dt><span class="section"><a href="boost_typetraits/reference/decay.html"> decay</a></span></dt>
|
||||
<dt><span class="section"><a href="boost_typetraits/reference/extent.html"> extent</a></span></dt>
|
||||
<dt><span class="section"><a href="boost_typetraits/reference/floating_point_promotion.html">
|
||||
@ -168,7 +171,7 @@
|
||||
</p>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"><p><small>Last revised: July 01, 2010 at 17:14:17 +0100</small></p></td>
|
||||
<td align="left"><p><small>Last revised: September 11, 2010 at 19:00:56 +0100</small></p></td>
|
||||
<td align="right"><div class="copyright-footer"></div></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
|
||||
@ -35,6 +35,9 @@ result of applying the transformation to the template argument `T`.
|
||||
template <class T>
|
||||
struct __add_volatile;
|
||||
|
||||
template <class... T>
|
||||
struct __common_type;
|
||||
|
||||
template <class T>
|
||||
struct __decay;
|
||||
|
||||
|
||||
@ -107,6 +107,7 @@
|
||||
[def __add_const [link boost_typetraits.reference.add_const add_const]]
|
||||
[def __add_volatile [link boost_typetraits.reference.add_volatile add_volatile]]
|
||||
[def __add_cv [link boost_typetraits.reference.add_cv add_cv]]
|
||||
[def __common_type [link boost_typetraits.reference.common_type common_type]]
|
||||
|
||||
[def __type_with_alignment [link boost_typetraits.reference.type_with_alignment type_with_alignment]]
|
||||
[def __aligned_storage [link boost_typetraits.reference.aligned_storage aligned_storage]]
|
||||
@ -171,6 +172,7 @@ that is the result of the transformation.
|
||||
[include add_volatile.qbk]
|
||||
[include aligned_storage.qbk]
|
||||
[include alignment_of.qbk]
|
||||
[include common_type.qbk]
|
||||
[include decay.qbk]
|
||||
[include extent.qbk]
|
||||
[include floating_point_promotion.qbk]
|
||||
|
||||
150
include/boost/type_traits/common_type.hpp
Normal file
150
include/boost/type_traits/common_type.hpp
Normal file
@ -0,0 +1,150 @@
|
||||
// common_type.hpp ---------------------------------------------------------//
|
||||
|
||||
// Copyright 2008 Howard Hinnant
|
||||
// Copyright 2008 Beman Dawes
|
||||
|
||||
// Distributed under the Boost Software License, Version 1.0.
|
||||
// See http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP
|
||||
#define BOOST_TYPE_TRAITS_COMMON_TYPE_HPP
|
||||
|
||||
#include <boost/config.hpp>
|
||||
|
||||
#ifdef __SUNPRO_CC
|
||||
# define BOOST_COMMON_TYPE_DONT_USE_TYPEOF
|
||||
#endif
|
||||
|
||||
//----------------------------------------------------------------------------//
|
||||
#if defined(BOOST_NO_VARIADIC_TEMPLATES)
|
||||
#define BOOST_COMMON_TYPE_ARITY 3
|
||||
#endif
|
||||
|
||||
//----------------------------------------------------------------------------//
|
||||
#if defined(BOOST_NO_DECLTYPE) && !defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
|
||||
#define BOOST_TYPEOF_SILENT
|
||||
#include <boost/typeof/typeof.hpp> // boost wonders never cease!
|
||||
#endif
|
||||
|
||||
//----------------------------------------------------------------------------//
|
||||
#ifndef BOOST_NO_STATIC_ASSERT
|
||||
#define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES) static_assert(CND,MSG)
|
||||
#elif defined(BOOST_COMMON_TYPE_USES_MPL_ASSERT)
|
||||
#include <boost/mpl/assert.hpp>
|
||||
#include <boost/mpl/bool.hpp>
|
||||
#define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES) \
|
||||
BOOST_MPL_ASSERT_MSG(boost::mpl::bool_< (CND) >::type::value, MSG, TYPES)
|
||||
#else
|
||||
#include <boost/static_assert.hpp>
|
||||
#define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES) BOOST_STATIC_ASSERT(CND)
|
||||
#endif
|
||||
|
||||
#if !defined(BOOST_NO_STATIC_ASSERT) || !defined(BOOST_COMMON_TYPE_USES_MPL_ASSERT)
|
||||
#define BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE "must be complete type"
|
||||
#endif
|
||||
|
||||
#if defined(BOOST_NO_DECLTYPE) && defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
|
||||
#include <boost/type_traits/detail/common_type_imp.hpp>
|
||||
#include <boost/type_traits/remove_cv.hpp>
|
||||
#endif
|
||||
#include <boost/mpl/if.hpp>
|
||||
//#include <boost/type_traits/declval.hpp>
|
||||
#include <boost/type_traits/add_rvalue_reference.hpp>
|
||||
|
||||
//----------------------------------------------------------------------------//
|
||||
// //
|
||||
// C++03 implementation of //
|
||||
// 20.6.7 Other transformations [meta.trans.other] //
|
||||
// Written by Howard Hinnant //
|
||||
// Adapted for Boost by Beman Dawes, Vicente Botet and Jeffrey Hellrung //
|
||||
// //
|
||||
//----------------------------------------------------------------------------//
|
||||
|
||||
namespace boost {
|
||||
|
||||
// prototype
|
||||
#if !defined(BOOST_NO_VARIADIC_TEMPLATES)
|
||||
template<typename... T>
|
||||
struct common_type;
|
||||
#else // or no specialization
|
||||
template <class T, class U = void, class V = void>
|
||||
struct common_type
|
||||
{
|
||||
public:
|
||||
typedef typename common_type<typename common_type<T, U>::type, V>::type type;
|
||||
};
|
||||
#endif
|
||||
|
||||
|
||||
// 1 arg
|
||||
template<typename T>
|
||||
#if !defined(BOOST_NO_VARIADIC_TEMPLATES)
|
||||
struct common_type<T>
|
||||
#else
|
||||
struct common_type<T, void, void>
|
||||
|
||||
#endif
|
||||
{
|
||||
BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(T) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (T));
|
||||
public:
|
||||
typedef T type;
|
||||
};
|
||||
|
||||
// 2 args
|
||||
namespace type_traits_detail {
|
||||
|
||||
template <class T, class U>
|
||||
struct common_type_2
|
||||
{
|
||||
private:
|
||||
BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(T) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (T));
|
||||
BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(U) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (U));
|
||||
static bool declval_bool(); // workaround gcc bug; not required by std
|
||||
static typename add_rvalue_reference<T>::type declval_T(); // workaround gcc bug; not required by std
|
||||
static typename add_rvalue_reference<U>::type declval_U(); // workaround gcc bug; not required by std
|
||||
static typename add_rvalue_reference<bool>::type declval_b();
|
||||
|
||||
#if !defined(BOOST_NO_DECLTYPE)
|
||||
public:
|
||||
typedef decltype(declval<bool>() ? declval<T>() : declval<U>()) type;
|
||||
#elif defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
|
||||
public:
|
||||
typedef typename detail_type_traits_common_type::common_type_impl<
|
||||
typename remove_cv<T>::type,
|
||||
typename remove_cv<U>::type
|
||||
>::type type;
|
||||
#else
|
||||
public:
|
||||
typedef BOOST_TYPEOF_TPL(declval_b() ? declval_T() : declval_U()) type;
|
||||
#endif
|
||||
};
|
||||
|
||||
template <class T>
|
||||
struct common_type_2<T, T>
|
||||
{
|
||||
typedef T type;
|
||||
};
|
||||
}
|
||||
|
||||
#if !defined(BOOST_NO_VARIADIC_TEMPLATES)
|
||||
template <class T, class U>
|
||||
struct common_type<T, U>
|
||||
#else
|
||||
template <class T, class U>
|
||||
struct common_type<T, U, void>
|
||||
#endif
|
||||
: type_traits_detail::common_type_2<T,U>
|
||||
{ };
|
||||
|
||||
|
||||
// 3 or more args
|
||||
#if !defined(BOOST_NO_VARIADIC_TEMPLATES)
|
||||
template<typename T, typename U, typename... V>
|
||||
struct common_type<T, U, V...> {
|
||||
public:
|
||||
typedef typename common_type<typename common_type<T, U>::type, V...>::type type;
|
||||
};
|
||||
#endif
|
||||
} // namespace boost
|
||||
|
||||
#endif // BOOST_TYPE_TRAITS_COMMON_TYPE_HPP
|
||||
304
include/boost/type_traits/detail/common_type_imp.hpp
Normal file
304
include/boost/type_traits/detail/common_type_imp.hpp
Normal file
@ -0,0 +1,304 @@
|
||||
/*******************************************************************************
|
||||
* boost/type_traits/detail/common_type_imp.hpp
|
||||
*
|
||||
* Copyright 2010, Jeffrey Hellrung.
|
||||
* 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)
|
||||
*
|
||||
* struct boost::common_type<T,U>
|
||||
*
|
||||
* common_type<T,U>::type is the type of the expression
|
||||
* b() ? x() : y()
|
||||
* where b() returns a bool, x() has return type T, and y() has return type U.
|
||||
* See
|
||||
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2661.htm#common_type
|
||||
*
|
||||
* Note that this evaluates to void if one or both of T and U is void.
|
||||
******************************************************************************/
|
||||
|
||||
#ifndef BOOST_TYPE_TRAITS_DETAIL_COMMON_TYPE_IMP_HPP
|
||||
#define BOOST_TYPE_TRAITS_DETAIL_COMMON_TYPE_IMP_HPP
|
||||
|
||||
#include <cstddef>
|
||||
|
||||
#include <boost/mpl/assert.hpp>
|
||||
#include <boost/mpl/at.hpp>
|
||||
#include <boost/mpl/begin_end.hpp>
|
||||
#include <boost/mpl/contains.hpp>
|
||||
#include <boost/mpl/copy.hpp>
|
||||
#include <boost/mpl/deref.hpp>
|
||||
#include <boost/mpl/eval_if.hpp>
|
||||
#include <boost/mpl/if.hpp>
|
||||
#include <boost/mpl/inserter.hpp>
|
||||
#include <boost/mpl/next.hpp>
|
||||
#include <boost/mpl/or.hpp>
|
||||
#include <boost/mpl/placeholders.hpp>
|
||||
#include <boost/mpl/push_back.hpp>
|
||||
#include <boost/mpl/size.hpp>
|
||||
#include <boost/mpl/vector/vector0.hpp>
|
||||
#include <boost/mpl/vector/vector10.hpp>
|
||||
#include <boost/type_traits/integral_constant.hpp>
|
||||
#include <boost/type_traits/is_enum.hpp>
|
||||
#include <boost/type_traits/is_integral.hpp>
|
||||
#include <boost/type_traits/make_signed.hpp>
|
||||
#include <boost/type_traits/make_unsigned.hpp>
|
||||
#include <boost/type_traits/remove_cv.hpp>
|
||||
#include <boost/type_traits/remove_reference.hpp>
|
||||
#include <boost/utility/declval.hpp>
|
||||
|
||||
namespace boost
|
||||
{
|
||||
|
||||
namespace detail_type_traits_common_type
|
||||
{
|
||||
|
||||
/*******************************************************************************
|
||||
* struct propagate_cv< From, To >
|
||||
*
|
||||
* This metafunction propagates cv-qualifiers on type From to type To.
|
||||
******************************************************************************/
|
||||
|
||||
template< class From, class To >
|
||||
struct propagate_cv
|
||||
{ typedef To type; };
|
||||
template< class From, class To >
|
||||
struct propagate_cv< const From, To >
|
||||
{ typedef To const type; };
|
||||
template< class From, class To >
|
||||
struct propagate_cv< volatile From, To >
|
||||
{ typedef To volatile type; };
|
||||
template< class From, class To >
|
||||
struct propagate_cv< const volatile From, To >
|
||||
{ typedef To const volatile type; };
|
||||
|
||||
/*******************************************************************************
|
||||
* struct is_signable_integral<T>
|
||||
*
|
||||
* This metafunction determines if T is an integral type which can be made
|
||||
* signed or unsigned.
|
||||
******************************************************************************/
|
||||
|
||||
template< class T >
|
||||
struct is_signable_integral
|
||||
: mpl::or_< is_integral<T>, is_enum<T> >
|
||||
{ };
|
||||
template<>
|
||||
struct is_signable_integral< bool >
|
||||
: false_type
|
||||
{ };
|
||||
|
||||
/*******************************************************************************
|
||||
* struct sizeof_t<N>
|
||||
* typedef ... yes_type
|
||||
* typedef ... no_type
|
||||
*
|
||||
* These types are integral players in the use of the "sizeof trick", i.e., we
|
||||
* can distinguish overload selection by inspecting the size of the return type
|
||||
* of the overload.
|
||||
******************************************************************************/
|
||||
|
||||
template< std::size_t N > struct sizeof_t { char _dummy[N]; };
|
||||
typedef sizeof_t<1> yes_type;
|
||||
typedef sizeof_t<2> no_type;
|
||||
BOOST_MPL_ASSERT_RELATION( sizeof( yes_type ), ==, 1 );
|
||||
BOOST_MPL_ASSERT_RELATION( sizeof( no_type ), ==, 2 );
|
||||
|
||||
/*******************************************************************************
|
||||
* rvalue_test(T&) -> no_type
|
||||
* rvalue_test(...) -> yes_type
|
||||
*
|
||||
* These overloads are used to determine the rvalue-ness of an expression.
|
||||
******************************************************************************/
|
||||
|
||||
template< class T > no_type rvalue_test(T&);
|
||||
yes_type rvalue_test(...);
|
||||
|
||||
/*******************************************************************************
|
||||
* struct conversion_test_overloads< Sequence >
|
||||
*
|
||||
* This struct has multiple overloads of the static member function apply, each
|
||||
* one taking a single parameter of a type within the Boost.MPL sequence
|
||||
* Sequence. Each such apply overload has a return type with sizeof equal to
|
||||
* one plus the index of the parameter type within Sequence. Thus, we can
|
||||
* deduce the type T of an expression as long as we can generate a finite set of
|
||||
* candidate types containing T via these apply overloads and the "sizeof
|
||||
* trick".
|
||||
******************************************************************************/
|
||||
|
||||
template< class First, class Last, std::size_t Index >
|
||||
struct conversion_test_overloads_iterate
|
||||
: conversion_test_overloads_iterate<
|
||||
typename mpl::next< First >::type, Last, Index + 1
|
||||
>
|
||||
{
|
||||
using conversion_test_overloads_iterate<
|
||||
typename mpl::next< First >::type, Last, Index + 1
|
||||
>::apply;
|
||||
static sizeof_t< Index + 1 >
|
||||
apply(typename mpl::deref< First >::type);
|
||||
};
|
||||
|
||||
template< class Last, std::size_t Index >
|
||||
struct conversion_test_overloads_iterate< Last, Last, Index >
|
||||
{ static sizeof_t< Index + 1 > apply(...); };
|
||||
|
||||
template< class Sequence >
|
||||
struct conversion_test_overloads
|
||||
: conversion_test_overloads_iterate<
|
||||
typename mpl::begin< Sequence >::type,
|
||||
typename mpl::end< Sequence >::type,
|
||||
0
|
||||
>
|
||||
{ };
|
||||
|
||||
/*******************************************************************************
|
||||
* struct select< Sequence, Index >
|
||||
*
|
||||
* select is synonymous with mpl::at_c unless Index equals the size of the
|
||||
* Boost.MPL Sequence, in which case this evaluates to void.
|
||||
******************************************************************************/
|
||||
|
||||
template<
|
||||
class Sequence, int Index,
|
||||
int N = mpl::size< Sequence >::value
|
||||
>
|
||||
struct select
|
||||
: mpl::at_c< Sequence, Index >
|
||||
{ };
|
||||
template< class Sequence, int N >
|
||||
struct select< Sequence, N, N >
|
||||
{ typedef void type; };
|
||||
|
||||
/*******************************************************************************
|
||||
* class deduce_common_type< T, U, NominalCandidates >
|
||||
* struct nominal_candidates<T,U>
|
||||
* struct common_type_dispatch_on_rvalueness<T,U>
|
||||
* struct common_type_impl<T,U>
|
||||
*
|
||||
* These classes and structs implement the logic behind common_type, which goes
|
||||
* roughly as follows. Let C be the type of the conditional expression
|
||||
* declval< bool >() ? declval<T>() : declval<U>()
|
||||
* if C is an rvalue, then:
|
||||
* let T' and U' be T and U stripped of reference- and cv-qualifiers
|
||||
* if T' and U' are pointer types, say, T' = V* and U' = W*, then:
|
||||
* define the set of NominalCandidates to be
|
||||
* { V*, W*, V'*, W'* }
|
||||
* where V' is V with whatever cv-qualifiers are on W, and W' is W
|
||||
* with whatever cv-qualifiers are on V
|
||||
* else T' and U' are both "signable integral types" (integral and enum
|
||||
* types excepting bool), then:
|
||||
* define the set of NominalCandidates to be
|
||||
* { unsigned(T'), unsigned(U'), signed(T'), signed(U') }
|
||||
* where unsigned(X) is make_unsigned<X>::type and signed(X) is
|
||||
* make_signed<X>::type
|
||||
* else
|
||||
* define the set of NominalCandidates to be
|
||||
* { T', U' }
|
||||
* else
|
||||
* let V and W be T and U stripped of reference-qualifiers
|
||||
* define the set of NominalCandidates to be
|
||||
* { V&, W&, V'&, W'& }
|
||||
* where V' is V with whatever cv-qualifiers are on W, and W' is W with
|
||||
* whatever cv-qualifiers are on V
|
||||
* define the set of Candidates to be equal to the set of NominalCandidates with
|
||||
* duplicates removed, and use this set of Candidates to determine C using the
|
||||
* conversion_test_overloads struct
|
||||
******************************************************************************/
|
||||
|
||||
template< class T, class U, class NominalCandidates >
|
||||
class deduce_common_type
|
||||
{
|
||||
typedef typename mpl::copy<
|
||||
NominalCandidates,
|
||||
mpl::inserter<
|
||||
mpl::vector0<>,
|
||||
mpl::if_<
|
||||
mpl::contains< mpl::_1, mpl::_2 >,
|
||||
mpl::_1,
|
||||
mpl::push_back< mpl::_1, mpl::_2 >
|
||||
>
|
||||
>
|
||||
>::type candidate_types;
|
||||
static const int best_candidate_index =
|
||||
sizeof( conversion_test_overloads< candidate_types >::apply(
|
||||
declval< bool >() ? declval<T>() : declval<U>()
|
||||
) ) - 1;
|
||||
public:
|
||||
typedef typename select< candidate_types, best_candidate_index >::type type;
|
||||
};
|
||||
|
||||
template<
|
||||
class T, class U,
|
||||
class V = typename remove_cv< typename remove_reference<T>::type >::type,
|
||||
class W = typename remove_cv< typename remove_reference<U>::type >::type,
|
||||
bool = is_signable_integral<V>::value && is_signable_integral<W>::value
|
||||
>
|
||||
struct nominal_candidates;
|
||||
|
||||
template< class T, class U, class V, class W >
|
||||
struct nominal_candidates< T, U, V, W, false >
|
||||
{ typedef mpl::vector2<V,W> type; };
|
||||
|
||||
template< class T, class U, class V, class W >
|
||||
struct nominal_candidates< T, U, V, W, true >
|
||||
{
|
||||
typedef mpl::vector4<
|
||||
typename make_unsigned<V>::type,
|
||||
typename make_unsigned<W>::type,
|
||||
typename make_signed<V>::type,
|
||||
typename make_signed<W>::type
|
||||
> type;
|
||||
};
|
||||
|
||||
template< class T, class U, class V, class W >
|
||||
struct nominal_candidates< T, U, V*, W*, false >
|
||||
{
|
||||
typedef mpl::vector4<
|
||||
V*, W*,
|
||||
typename propagate_cv<W,V>::type *,
|
||||
typename propagate_cv<V,W>::type *
|
||||
> type;
|
||||
};
|
||||
|
||||
template<class T, class U, bool b>
|
||||
struct common_type_dispatch_on_rvalueness;
|
||||
|
||||
template< class T, class U >
|
||||
struct common_type_dispatch_on_rvalueness< T, U, true >
|
||||
: deduce_common_type< T, U, typename nominal_candidates<T,U>::type >
|
||||
{ };
|
||||
|
||||
template< class T, class U >
|
||||
struct common_type_dispatch_on_rvalueness< T, U, false >
|
||||
{
|
||||
private:
|
||||
typedef typename remove_reference<T>::type unrefed_T_type;
|
||||
typedef typename remove_reference<U>::type unrefed_U_type;
|
||||
public:
|
||||
typedef typename deduce_common_type<
|
||||
T, U,
|
||||
mpl::vector4<
|
||||
unrefed_T_type &,
|
||||
unrefed_U_type &,
|
||||
typename propagate_cv< unrefed_U_type, unrefed_T_type >::type &,
|
||||
typename propagate_cv< unrefed_T_type, unrefed_U_type >::type &
|
||||
>
|
||||
>::type type;
|
||||
};
|
||||
|
||||
template< class T, class U >
|
||||
struct common_type_impl
|
||||
: common_type_dispatch_on_rvalueness<T,U, sizeof( ::boost::detail_type_traits_common_type::rvalue_test(
|
||||
declval< bool >() ? declval<T>() : declval<U>() ) ) == sizeof( yes_type ) >
|
||||
{ };
|
||||
|
||||
template< class T > struct common_type_impl< T, void > { typedef void type; };
|
||||
template< class T > struct common_type_impl< void, T > { typedef void type; };
|
||||
template<> struct common_type_impl< void, void > { typedef void type; };
|
||||
|
||||
} // namespace detail_type_traits_common_type
|
||||
|
||||
|
||||
} // namespace boost
|
||||
|
||||
#endif // BOOST_TYPE_TRAITS_DETAIL_COMMON_TYPE_HPP
|
||||
@ -32,5 +32,7 @@ rule all-tests {
|
||||
|
||||
test-suite type_traits : [ all-tests ] ;
|
||||
|
||||
compile-fail common_type_fail.cpp ;
|
||||
|
||||
|
||||
|
||||
|
||||
@ -16,10 +16,23 @@
|
||||
# include <boost/type_traits/alignment_of.hpp>
|
||||
#endif
|
||||
|
||||
//
|
||||
// Need to defined some member functions for empty_UDT,
|
||||
// we don't want to put these in the test.hpp as that
|
||||
// causes overly-clever compilers to figure out that they can't throw
|
||||
// which in turn breaks other tests.
|
||||
//
|
||||
empty_UDT::empty_UDT(){}
|
||||
empty_UDT::~empty_UDT(){}
|
||||
empty_UDT::empty_UDT(const empty_UDT&){}
|
||||
empty_UDT& empty_UDT::operator=(const empty_UDT&){ return *this; }
|
||||
bool empty_UDT::operator==(const empty_UDT&)const{ return true; }
|
||||
|
||||
|
||||
//
|
||||
// VC++ emits an awful lot of warnings unless we define these:
|
||||
#ifdef BOOST_MSVC
|
||||
# pragma warning(disable:4244)
|
||||
# pragma warning(disable:4244 4121)
|
||||
//
|
||||
// What follows here is the test case for issue 1946.
|
||||
//
|
||||
28
test/common_type_fail.cpp
Normal file
28
test/common_type_fail.cpp
Normal file
@ -0,0 +1,28 @@
|
||||
// common_type_test.cpp ----------------------------------------------------//
|
||||
|
||||
// Copyright 2010 Beman Dawes
|
||||
|
||||
// Distributed under the Boost Software License, Version 1.0.
|
||||
// See http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#define _CRT_SECURE_NO_WARNINGS // disable VC++ foolishness
|
||||
|
||||
#include "test.hpp"
|
||||
#ifndef TEST_STD
|
||||
#include <boost/type_traits/common_type.hpp>
|
||||
#else
|
||||
#include <type_traits>
|
||||
#endif
|
||||
|
||||
struct C1 {
|
||||
//~ private:
|
||||
//~ C1();
|
||||
};
|
||||
|
||||
struct C2 {};
|
||||
|
||||
|
||||
|
||||
typedef tt::common_type<C1, C2>::type AC;
|
||||
|
||||
|
||||
103
test/common_type_test.cpp
Normal file
103
test/common_type_test.cpp
Normal file
@ -0,0 +1,103 @@
|
||||
// common_type_test.cpp ----------------------------------------------------//
|
||||
|
||||
// Copyright 2010 Beman Dawes
|
||||
|
||||
// Distributed under the Boost Software License, Version 1.0.
|
||||
// See http://www.boost.org/LICENSE_1_0.txt
|
||||
|
||||
#include "test.hpp"
|
||||
#include "check_type.hpp"
|
||||
#ifdef TEST_STD
|
||||
# include <type_traits>
|
||||
#else
|
||||
# include <boost/type_traits/common_type.hpp>
|
||||
#endif
|
||||
#include <iostream>
|
||||
|
||||
struct C1 {};
|
||||
|
||||
struct C2 {};
|
||||
|
||||
|
||||
struct C3 : C2 {};
|
||||
struct C1C2 {
|
||||
C1C2() {}
|
||||
C1C2(C1 const&) {}
|
||||
C1C2(C2 const&) {}
|
||||
C1C2& operator=(C1C2 const&) {
|
||||
return *this;
|
||||
}
|
||||
};
|
||||
|
||||
template <typename C, typename A>
|
||||
void proc2(typename boost::common_type<A, C>::type const& ) {}
|
||||
|
||||
template <typename C, typename A, typename B>
|
||||
void proc3(typename boost::common_type<C, A, B>::type const& ) {}
|
||||
|
||||
template <typename C, typename A>
|
||||
void assignation_2() {
|
||||
typedef typename boost::common_type<A, C>::type AC;
|
||||
A a;
|
||||
C c;
|
||||
AC ac;
|
||||
ac=a;
|
||||
ac=c;
|
||||
|
||||
proc2<C, A>(a);
|
||||
proc2<C, A>(c);
|
||||
|
||||
}
|
||||
|
||||
template <typename C, typename A, typename B>
|
||||
void assignation_3() {
|
||||
typedef typename boost::common_type<C, A, B>::type ABC;
|
||||
A a;
|
||||
B b;
|
||||
C c;
|
||||
ABC abc;
|
||||
|
||||
abc=a;
|
||||
abc=b;
|
||||
abc=c;
|
||||
|
||||
proc3<C, A, B>(a);
|
||||
proc3<C, A, B>(b);
|
||||
proc3<C, A, B>(c);
|
||||
}
|
||||
|
||||
C1C2 c1c2;
|
||||
C1 c1;
|
||||
|
||||
int f(C1C2 ) { return 1;}
|
||||
int f(C1 ) { return 2;}
|
||||
template <typename OSTREAM>
|
||||
OSTREAM& operator<<(OSTREAM& os, C1 const&) {return os;}
|
||||
|
||||
C1C2& declval_C1C2() {return c1c2;}
|
||||
C1& declval_C1(){return c1;}
|
||||
bool declval_bool(){return true;}
|
||||
|
||||
|
||||
TT_TEST_BEGIN(common_type)
|
||||
{
|
||||
assignation_2<C1C2, C1>();
|
||||
typedef tt::common_type<C1C2&, C1&>::type T1;
|
||||
typedef tt::common_type<C3*, C2*>::type T2;
|
||||
typedef tt::common_type<int*, int const*>::type T3;
|
||||
#if defined(BOOST_NO_DECLTYPE) && !defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
|
||||
// fails if BOOST_COMMON_TYPE_DONT_USE_TYPEOF:
|
||||
typedef tt::common_type<int volatile*, int const*>::type T4;
|
||||
#endif
|
||||
typedef tt::common_type<int*, int volatile*>::type T5;
|
||||
|
||||
assignation_2<C1, C1C2>();
|
||||
assignation_2<C1C2, C2>();
|
||||
assignation_2<C2, C1C2>();
|
||||
assignation_3<C1, C1C2, C2>();
|
||||
assignation_3<C1C2, C1, C2>();
|
||||
assignation_3<C2, C1C2, C1>();
|
||||
assignation_3<C1C2, C2, C1>();
|
||||
//assignation_3<C1, C2, C1C2>(); // fails because the common type is the third
|
||||
}
|
||||
TT_TEST_END
|
||||
Reference in New Issue
Block a user