1/////////////////////////////////////////////////////////////////////
2// Copyright 2018 Glen Joseph Fernandes.
3// Copyright 2021 Matt Borland. Distributed under the Boost
4// Software License, Version 1.0. (See accompanying file
5// LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt
6
7#ifndef BOOST_MP_DETAIL_EMPTY_VALUE_HPP
8#define BOOST_MP_DETAIL_EMPTY_VALUE_HPP
9
10#include <utility>
11#include <boost/multiprecision/detail/standalone_config.hpp>
12
13#if defined(BOOST_GCC_VERSION) && (BOOST_GCC_VERSION >= 40700)
14#define BOOST_DETAIL_EMPTY_VALUE_BASE
15#elif defined(BOOST_INTEL) && defined(_MSC_VER) && (_MSC_VER >= 1800)
16#define BOOST_DETAIL_EMPTY_VALUE_BASE
17#elif defined(BOOST_MSVC) && (BOOST_MSVC >= 1800)
18#define BOOST_DETAIL_EMPTY_VALUE_BASE
19#elif defined(BOOST_CLANG) && !defined(__CUDACC__)
20#if __has_feature(is_empty) && __has_feature(is_final)
21#define BOOST_DETAIL_EMPTY_VALUE_BASE
22#endif
23#endif
24
25namespace boost { namespace multiprecision { namespace detail {
26
27template <typename T>
28struct use_empty_value_base
29{
30#if defined(BOOST_DETAIL_EMPTY_VALUE_BASE)
31 static constexpr bool value = __is_empty(T) && !__is_final(T);
32#else
33 static constexpr bool value = false;
34#endif
35};
36
37struct empty_init_t {};
38
39namespace empty_impl {
40
41template <typename T, unsigned N = 0,
42 bool E = boost::multiprecision::detail::use_empty_value_base<T>::value>
43class empty_value
44{
45private:
46 T value_;
47
48public:
49 using type = T;
50
51 empty_value() = default;
52 explicit empty_value(boost::multiprecision::detail::empty_init_t) : value_ {} {}
53
54 template <typename U, typename... Args>
55 empty_value(boost::multiprecision::detail::empty_init_t, U&& value, Args&&... args) :
56 value_ {std::forward<U>(value), std::forward<Args>(args)...} {}
57
58 const T& get() const noexcept { return value_; }
59 T& get() noexcept { return value_; }
60};
61
62template <typename T, unsigned N>
63class empty_value<T, N, true> : T
64{
65public:
66 using type = T;
67
68 empty_value() = default;
69 explicit empty_value(boost::multiprecision::detail::empty_init_t) : T{} {}
70
71 template <typename U, typename... Args>
72 empty_value(boost::multiprecision::detail::empty_init_t, U&& value, Args&&... args) :
73 T{std::forward<U>(value), std::forward<Args>(args)...} {}
74
75 const T& get() const noexcept { return *this; }
76 T& get() noexcept { return *this; }
77};
78
79} // Namespace empty impl
80
81using empty_impl::empty_value;
82
83BOOST_INLINE_CONSTEXPR empty_init_t empty_init = empty_init_t();
84
85}}} // Namespaces
86
87#endif // BOOST_MP_DETAIL_EMPTY_VALUE_HPP
88

source code of boost/libs/multiprecision/include/boost/multiprecision/detail/empty_value.hpp