1// Boost.Range library
2//
3// Copyright Arno Schoedl & Neil Groves 2009.
4// Use, modification and distribution is subject to the Boost Software
5// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
6// http://www.boost.org/LICENSE_1_0.txt)
7//
8// For more information, see http://www.boost.org/libs/range/
9//
10#ifndef BOOST_RANGE_DETAIL_EXTRACT_OPTIONAL_TYPE_HPP_INCLUDED
11#define BOOST_RANGE_DETAIL_EXTRACT_OPTIONAL_TYPE_HPP_INCLUDED
12
13#if defined(_MSC_VER)
14# pragma once
15#endif
16
17#include <boost/config.hpp>
18#include <boost/preprocessor/cat.hpp>
19#include <boost/mpl/has_xxx.hpp>
20
21#if !defined(BOOST_MPL_CFG_NO_HAS_XXX)
22
23// Defines extract_some_typedef<T> which exposes T::some_typedef as
24// extract_some_typedef<T>::type if T::some_typedef exists. Otherwise
25// extract_some_typedef<T> is empty.
26#define BOOST_RANGE_EXTRACT_OPTIONAL_TYPE( a_typedef ) \
27 BOOST_MPL_HAS_XXX_TRAIT_DEF(a_typedef) \
28 template< typename C, bool B = BOOST_PP_CAT(has_, a_typedef)<C>::value > \
29 struct BOOST_PP_CAT(extract_, a_typedef) \
30 {}; \
31 template< typename C > \
32 struct BOOST_PP_CAT(extract_, a_typedef)< C, true > \
33 { \
34 typedef BOOST_DEDUCED_TYPENAME C::a_typedef type; \
35 };
36
37#else
38
39#define BOOST_RANGE_EXTRACT_OPTIONAL_TYPE( a_typedef ) \
40 template< typename C > \
41 struct BOOST_PP_CAT(extract_, a_typedef) \
42 { \
43 typedef BOOST_DEDUCED_TYPENAME C::a_typedef type; \
44 };
45
46#endif
47
48#endif // include guard
49

source code of include/boost/range/detail/extract_optional_type.hpp