130 lines
2.9 KiB
ReStructuredText
130 lines
2.9 KiB
ReStructuredText
.. Metafunctions/Invocation//apply_wrap |20
|
|
|
|
apply_wrap
|
|
==========
|
|
|
|
Synopsis
|
|
--------
|
|
|
|
.. parsed-literal::
|
|
|
|
template<
|
|
typename F
|
|
>
|
|
struct apply_wrap0
|
|
{
|
|
typedef |unspecified| type;
|
|
};
|
|
|
|
template<
|
|
typename F, typename A1
|
|
>
|
|
struct apply_wrap1
|
|
{
|
|
typedef |unspecified| type;
|
|
};
|
|
|
|
|...|
|
|
|
|
template<
|
|
typename F, typename A1,\ |...| typename An
|
|
>
|
|
struct apply_wrap\ *n*
|
|
{
|
|
typedef |unspecified| type;
|
|
};
|
|
|
|
|
|
|
|
Description
|
|
-----------
|
|
|
|
Invokes a |Metafunction Class| ``F`` with arguments ``A1``,... ``An``.
|
|
|
|
In essence, ``apply_wrap`` forms are nothing more than syntactic wrappers around
|
|
``F::apply<A1,... An>::type`` / ``F::apply::type`` expressions (hence the name).
|
|
They provide a more concise notation and higher portability than their
|
|
underlaying constructs at the cost of an extra template instantiation.
|
|
|
|
|
|
Header
|
|
------
|
|
|
|
.. parsed-literal::
|
|
|
|
#include <boost/mpl/apply_wrap.hpp>
|
|
|
|
|
|
Parameters
|
|
----------
|
|
|
|
+---------------+-----------------------------------+-----------------------------------------------+
|
|
| Parameter | Requirement | Description |
|
|
+===============+===================================+===============================================+
|
|
| ``F`` | |Metafunction Class| | A metafunction class to invoke. |
|
|
+---------------+-----------------------------------+-----------------------------------------------+
|
|
| |A1...An| | Any type | Invocation arguments. |
|
|
+---------------+-----------------------------------+-----------------------------------------------+
|
|
|
|
|
|
Expression semantics
|
|
--------------------
|
|
|
|
For any |Metafunction Class| ``f`` and arbitrary types |a1...an|:
|
|
|
|
|
|
.. parsed-literal::
|
|
|
|
typedef apply_wrap\ *n*\ <f,a1,\ |...|\ an>::type t;
|
|
|
|
:Return type:
|
|
Any type.
|
|
|
|
:Semantics:
|
|
If ``n > 0``, equivalent to ``typedef f::apply<a1,... an>::type t;``,
|
|
otherwise equivalent to either ``typedef f::apply::type t;`` or
|
|
``typedef f::apply<>::type t;`` depending on whether ``f::apply`` is
|
|
a class or a class template.
|
|
|
|
|
|
Example
|
|
-------
|
|
|
|
.. parsed-literal::
|
|
|
|
struct f0
|
|
{
|
|
template< typename T = int > struct apply
|
|
{
|
|
typedef char type;
|
|
};
|
|
};
|
|
|
|
struct g0
|
|
{
|
|
struct apply { typedef char type; };
|
|
};
|
|
|
|
struct f2
|
|
{
|
|
template< typename T1, typename T2 > struct apply
|
|
{
|
|
typedef T2 type;
|
|
};
|
|
};
|
|
|
|
|
|
typedef apply_wrap\ ``0``\ < f0 >::type r1;
|
|
typedef apply_wrap\ ``0``\ < g0 >::type r2;
|
|
typedef apply_wrap\ ``2``\ < f2,int,char >::type r3;
|
|
|
|
BOOST_MPL_ASSERT(( is_same<r1,char> ));
|
|
BOOST_MPL_ASSERT(( is_same<r2,char> ));
|
|
BOOST_MPL_ASSERT(( is_same<r3,char> ));
|
|
|
|
|
|
See also
|
|
--------
|
|
|
|
|Metafunctions|, |Invocation|, |apply|, |lambda|, |quote|, |bind|, |protect|
|