1 /*=============================================================================
2     Copyright (c) 2016 Paul Fultz II
3     result_type.hpp
4     Distributed under the Boost Software License, Version 1.0. (See accompanying
5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 ==============================================================================*/
7 
8 #ifndef BOOST_HOF_GUARD_RESULT_TYPE_HPP
9 #define BOOST_HOF_GUARD_RESULT_TYPE_HPP
10 
11 #include <boost/hof/detail/holder.hpp>
12 #include <utility>
13 
14 namespace boost { namespace hof { namespace detail {
15 
16 template<class F, class=void>
17 struct function_result_type
18 {};
19 
20 template<class F>
21 struct function_result_type<F, typename holder<
22     typename F::result_type
23 >::type>
24 {
25     typedef typename F::result_type result_type;
26 };
27 
28 template<class F, class G, class=void>
29 struct compose_function_result_type
30 : function_result_type<F>
31 {};
32 
33 template<class F, class G>
34 struct compose_function_result_type<F, G, typename holder<
35     decltype(std::declval<F>()(std::declval<typename G::result_type>()))
36 >::type>
37 {
38     typedef decltype(std::declval<F>()(std::declval<typename G::result_type>())) result_type;
39 };
40 
41 }}} // namespace boost::hof
42 
43 #endif
44