| .. Metafunctions/Miscellaneous//always |20 |
| |
| always |
| ====== |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename X |
| > |
| struct always |
| { |
| // |unspecified| |
| // |...| |
| }; |
| |
| |
| Description |
| ----------- |
| |
| ``always<X>`` specialization is a variadic |Metafunction Class| always returning the |
| same type, ``X``, regardless of the number and types of passed arguments. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/always.hpp> |
| |
| Model of |
| -------- |
| |
| |Metafunction Class| |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+-------------------+-----------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+===================+===================================+ |
| | ``X`` | Any type | A type to be returned. | |
| +---------------+-------------------+-----------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For an arbitrary type ``x``: |
| |
| |
| .. parsed-literal:: |
| |
| typedef always<x> f; |
| |
| :Return type: |
| |Metafunction Class|. |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| struct f : bind< identity<_1>, x > {}; |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| typedef always<true\_> always_true; |
| |
| BOOST_MPL_ASSERT(( apply< always_true,false\_> )); |
| BOOST_MPL_ASSERT(( apply< always_true,false\_,false\_ > )); |
| BOOST_MPL_ASSERT(( apply< always_true,false\_,false\_,false\_ > )); |
| |
| |
| See also |
| -------- |
| |
| |Metafunctions|, |Metafunction Class|, |identity|, |bind|, |apply| |
| |
| |
| .. copyright:: Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams |
| 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) |
