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 
17 namespace boost
18 {
19     namespace range_detail
20     {
21 
22 template<typename F, typename R>
23 class default_constructible_unary_fn_wrapper
24 {
25 public:
26     typedef R result_type;
27 
default_constructible_unary_fn_wrapper()28     default_constructible_unary_fn_wrapper()
29     {
30     }
default_constructible_unary_fn_wrapper(const F & source)31     default_constructible_unary_fn_wrapper(const F& source)
32         : m_impl(source)
33     {
34     }
default_constructible_unary_fn_wrapper(const default_constructible_unary_fn_wrapper & source)35     default_constructible_unary_fn_wrapper(const default_constructible_unary_fn_wrapper& source)
36         : m_impl(source.m_impl)
37     {
38     }
operator =(const default_constructible_unary_fn_wrapper & source)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>
operator ()(const Arg & arg) const53     R operator()(const Arg& arg) const
54     {
55         BOOST_ASSERT(m_impl);
56         return (*m_impl)(arg);
57     }
58     template<typename Arg>
operator ()(Arg & arg) const59     R operator()(Arg& arg) const
60     {
61         BOOST_ASSERT(m_impl);
62         return (*m_impl)(arg);
63     }
64 private:
65     boost::optional<F> m_impl;
66 };
67 
68 template<typename F, typename R>
69 struct 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