| .. Metafunctions/Composition and Argument Binding//quote |40 |
| |
| quote |
| ===== |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| template< typename P1 > class F |
| , typename Tag = |unspecified| |
| > |
| struct quote1 |
| { |
| // |unspecified| |
| // |...| |
| }; |
| |
| |...| |
| |
| template< |
| template< typename P1,\ |...| typename P\ *n* > class F |
| , typename Tag = |unspecified| |
| > |
| struct quote\ *n* |
| { |
| // |unspecified| |
| // |...| |
| }; |
| |
| |
| Description |
| ----------- |
| |
| ``quote``\ *n* is a higher-order primitive that wraps an *n*-ary |Metafunction| to create |
| a corresponding |Metafunction Class|. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/quote.hpp> |
| |
| |
| Model of |
| -------- |
| |
| |Metafunction Class| |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+-----------------------+-----------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+=======================+===============================================+ |
| | ``F`` | |Metafunction| | A metafunction to wrap. | |
| +---------------+-----------------------+-----------------------------------------------+ |
| | ``Tag`` | Any type | A tag determining wrap semantics. | |
| +---------------+-----------------------+-----------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For any *n*-ary |Metafunction| ``f`` and arbitrary type ``tag``: |
| |
| |
| .. parsed-literal:: |
| |
| typedef quote\ *n*\ <f> g; |
| typedef quote\ *n*\ <f,tag> g; |
| |
| :Return type: |
| |Metafunction Class| |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| struct g |
| { |
| template< typename A1,\ |...| typename A\ *n* > struct apply |
| : f<A1,\ |...|\ A\ *n*\ > |
| { |
| }; |
| }; |
| |
| if ``f<A1,...An>`` has a nested type member ``::type``, and to |
| |
| .. parsed-literal:: |
| |
| struct g |
| { |
| template< typename A1,\ |...| typename A\ *n* > struct apply |
| { |
| typedef f<A1,\ |...|\ A\ *n*\ > type; |
| }; |
| }; |
| |
| otherwise. |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| template< typename T > struct f1 |
| { |
| typedef T type; |
| }; |
| |
| template< |
| typename T1, typename T2, typename T3, typename T4, typename T5 |
| > |
| struct f5 |
| { |
| // no 'type' member! |
| }; |
| |
| typedef quote\ ``1``\<f1>::apply<int>::type t1; |
| typedef quote\ ``5``\<f5>::apply<char,short,int,long,float>::type t5; |
| |
| BOOST_MPL_ASSERT(( is_same< t1, int > )); |
| BOOST_MPL_ASSERT(( is_same< t5, f5<char,short,int,long,float> > )); |
| |
| |
| See also |
| -------- |
| |
| |Composition and Argument Binding|, |Invocation|, |bind|, |lambda|, |protect|, |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) |
