1/*=============================================================================
2 Copyright (c) 2015 Paul Fultz II
3 static_const_var.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_STATIC_CONST_H
9#define BOOST_HOF_GUARD_STATIC_CONST_H
10
11#include <boost/hof/detail/intrinsics.hpp>
12
13namespace boost { namespace hof { namespace detail {
14
15template<class T>
16struct static_const_storage
17{
18 static constexpr T value = T();
19};
20
21template<class T>
22constexpr T static_const_storage<T>::value;
23
24struct static_const_var_factory
25{
26 constexpr static_const_var_factory()
27 {}
28
29 template<class T>
30 constexpr const T& operator=(const T&) const
31 {
32 static_assert(BOOST_HOF_IS_DEFAULT_CONSTRUCTIBLE(T), "Static const variable must be default constructible");
33 return static_const_storage<T>::value;
34 }
35};
36}
37
38template<class T>
39constexpr const T& static_const_var()
40{
41 return detail::static_const_storage<T>::value;
42}
43
44
45}} // namespace boost::hof
46
47#if BOOST_HOF_HAS_RELAXED_CONSTEXPR || defined(_MSC_VER)
48#define BOOST_HOF_STATIC_CONSTEXPR const constexpr
49#else
50#define BOOST_HOF_STATIC_CONSTEXPR static constexpr
51#endif
52
53#if defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7
54#define BOOST_HOF_STATIC_AUTO_REF extern __attribute__((weak)) constexpr auto
55#else
56#define BOOST_HOF_STATIC_AUTO_REF static constexpr auto&
57#endif
58
59// On gcc 4.6 use weak variables
60#if defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7
61#define BOOST_HOF_STATIC_CONST_VAR(name) extern __attribute__((weak)) constexpr auto name
62#else
63#define BOOST_HOF_STATIC_CONST_VAR(name) static constexpr auto& name = boost::hof::detail::static_const_var_factory()
64#endif
65
66#define BOOST_HOF_DECLARE_STATIC_VAR(name, ...) BOOST_HOF_STATIC_CONST_VAR(name) = __VA_ARGS__{}
67
68#endif
69

source code of boost/libs/hof/include/boost/hof/detail/static_const_var.hpp