1 // Copyright David Abrahams 2006. Distributed under the Boost
2 // Software License, Version 1.0. (See accompanying
3 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
4 #ifndef BOOST_DETAIL_FUNCTION1_DWA200655_HPP
5 # define BOOST_DETAIL_FUNCTION1_DWA200655_HPP
7 # include <boost/concept_check.hpp>
8 # include <boost/type_traits/remove_reference.hpp>
9 # include <boost/type_traits/add_const.hpp>
10 # include <boost/mpl/apply.hpp>
12 namespace boost { namespace detail {
14 // A utility for creating unary function objects that play nicely with
15 // boost::result_of and that handle the forwarding problem.
17 // mpl::apply<F, A0>::type is expected to be a stateless function
18 // object that accepts an argument of type A0&. It is also expected
19 // to have a nested ::result_type identical to its return type.
23 template<typename Signature>
27 template<typename This, typename A0>
28 struct result<This(A0)>
30 // How adding const to arguments handles rvalues.
32 // if A0 is arg0 is represents actual argument
33 // -------- ------- --------------------------
34 // T const & T const const T lvalue
35 // T & T non-const T lvalue
36 // T const T const const T rvalue
37 // T T const non-const T rvalue
38 typedef typename remove_reference<
39 typename add_const< A0 >::type
42 typedef typename mpl::apply1<F, arg0>::type impl;
43 typedef typename impl::result_type type;
46 // Handles mutable lvalues
48 typename result<function1(A0 &)>::type
49 operator ()(A0 &a0) const
51 typedef typename result<function1(A0 &)>::impl impl;
52 typedef typename result<function1(A0 &)>::type type;
54 BOOST_CONCEPT_ASSERT((UnaryFunction<impl, type, arg0>));
55 //boost::function_requires<UnaryFunctionConcept<impl, type, arg0> >();
59 // Handles const lvalues and all rvalues
61 typename result<function1(A0 const &)>::type
62 operator ()(A0 const &a0) const
64 typedef typename result<function1(A0 const &)>::impl impl;
65 typedef typename result<function1(A0 const &)>::type type;
66 typedef A0 const &arg0;
67 BOOST_CONCEPT_ASSERT((UnaryFunction<impl, type, arg0>));
68 //boost::function_requires<UnaryFunctionConcept<impl, type, arg0> >();
73 }} // namespace boost::detail
75 #endif // BOOST_DETAIL_FUNCTION1_DWA200655_HPP