1// Boost.Range library
2//
3// Copyright Neil Groves 2014. Use, modification and
4// distribution is subject to the Boost Software License, Version
5// 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_DEFAULT_CONSTRUCTIBLE_UNARY_FN_HPP_INCLUDED
11#define BOOST_RANGE_DETAIL_DEFAULT_CONSTRUCTIBLE_UNARY_FN_HPP_INCLUDED
12
13#include <boost/optional/optional.hpp>
14#include <boost/mpl/if.hpp>
15#include <boost/type_traits/has_trivial_constructor.hpp>
16
17namespace boost
18{
19 namespace range_detail
20 {
21
22template<typename F, typename R>
23class default_constructible_unary_fn_wrapper
24{
25public:
26 typedef R result_type;
27
28 default_constructible_unary_fn_wrapper()
29 {
30 }
31 default_constructible_unary_fn_wrapper(const F& source)
32 : m_impl(source)
33 {
34 }
35 default_constructible_unary_fn_wrapper(const default_constructible_unary_fn_wrapper& source)
36 : m_impl(source.m_impl)
37 {
38 }
39 default_constructible_unary_fn_wrapper& operator=(const default_constructible_unary_fn_wrapper& source)
40 {
41 if (source.m_impl)
42 {
43 // Lambda are not copy/move assignable.
44 m_impl.emplace(*source.m_impl);
45 }
46 else
47 {
48 m_impl.reset();
49 }
50 return *this;
51 }
52 template<typename Arg>
53 R operator()(const Arg& arg) const
54 {
55 BOOST_ASSERT(m_impl);
56 return (*m_impl)(arg);
57 }
58 template<typename Arg>
59 R operator()(Arg& arg) const
60 {
61 BOOST_ASSERT(m_impl);
62 return (*m_impl)(arg);
63 }
64private:
65 boost::optional<F> m_impl;
66};
67
68template<typename F, typename R>
69struct default_constructible_unary_fn_gen
70{
71 typedef typename boost::mpl::if_<
72 boost::has_trivial_default_constructor<F>,
73 F,
74 default_constructible_unary_fn_wrapper<F,R>
75 >::type type;
76};
77
78 } // namespace range_detail
79} // namespace boost
80
81#endif // include guard
82

source code of boost/libs/range/include/boost/range/detail/default_constructible_unary_fn.hpp