1 /*=============================================================================
2     Copyright (c) 2015 Paul Fultz II
3     constexpr_deduce.h
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_FUNCTION_CONSTEXPR_DEDUCE_H
9 #define BOOST_HOF_GUARD_FUNCTION_CONSTEXPR_DEDUCE_H
10 
11 #include <boost/hof/config.hpp>
12 
13 #define BOOST_HOF_CONST_FOLD(x) (__builtin_constant_p(x) ? (x) : (x))
14 
15 #ifndef BOOST_HOF_HAS_CONST_FOLD
16 #if defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7
17 #define BOOST_HOF_HAS_CONST_FOLD 0
18 #elif defined(__clang__) || defined (__GNUC__)
19 #define BOOST_HOF_HAS_CONST_FOLD 1
20 #else
21 #define BOOST_HOF_HAS_CONST_FOLD 0
22 #endif
23 #endif
24 
25 
26 namespace boost { namespace hof {
27 
28 namespace detail {
29 
30 struct constexpr_deduce
31 {
constexpr_deduceboost::hof::detail::constexpr_deduce32     constexpr constexpr_deduce()
33     {}
34     template<class F>
operator Fboost::hof::detail::constexpr_deduce35     constexpr operator F() const
36     {
37         return F();
38     }
39 };
40 
41 template<class T>
42 struct constexpr_deduce_unique
43 {
constexpr_deduce_uniqueboost::hof::detail::constexpr_deduce_unique44     constexpr constexpr_deduce_unique()
45     {}
46 #if BOOST_HOF_HAS_CONST_FOLD
47     template<class F>
operator const F&boost::hof::detail::constexpr_deduce_unique48     constexpr operator const F&() const
49     {
50         static_assert(BOOST_HOF_IS_EMPTY(F), "Function or lambda expression must be empty");
51         return BOOST_HOF_CONST_FOLD(reinterpret_cast<const F&>(static_const_var<T>()));
52     }
53 #else
54     template<class F>
operator Fboost::hof::detail::constexpr_deduce_unique55     constexpr operator F() const
56     {
57         // static_assert(std::is_default_constructible<F>::value, "Function not default constructible");
58         return F();
59     }
60 #endif
61 };
62 
63 }}} // namespace boost::hof
64 
65 #define BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE true ? boost::hof::detail::constexpr_deduce() :
66 #define BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE_UNIQUE(T) true ? boost::hof::detail::constexpr_deduce_unique<T>() :
67 
68 #ifdef _MSC_VER
69 #define BOOST_HOF_DETAIL_MSVC_CONSTEXPR_DEDUCE BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE
70 #else
71 #define BOOST_HOF_DETAIL_MSVC_CONSTEXPR_DEDUCE
72 #endif
73 
74 #endif
75