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Copy pathempty_value.hpp
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136 lines (112 loc) · 2.93 KB
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/*
Copyright 2018 Glen Joseph Fernandes
(glenjofe@gmail.com)
Distributed under the Boost Software License, Version 1.0.
(http://www.boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_CORE_EMPTY_VALUE_HPP
#define BOOST_CORE_EMPTY_VALUE_HPP
#include <boost/config.hpp>
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
#include <utility>
#endif
#if defined(BOOST_GCC_VERSION) && (BOOST_GCC_VERSION >= 40700)
#define BOOST_DETAIL_EMPTY_VALUE_BASE
#elif defined(BOOST_INTEL) && defined(_MSC_VER) && (_MSC_VER >= 1800)
#define BOOST_DETAIL_EMPTY_VALUE_BASE
#elif defined(BOOST_MSVC) && (BOOST_MSVC >= 1800)
#define BOOST_DETAIL_EMPTY_VALUE_BASE
#elif defined(BOOST_CLANG) && !defined(__CUDACC__)
#if __has_feature(is_empty) && __has_feature(is_final)
#define BOOST_DETAIL_EMPTY_VALUE_BASE
#endif
#endif
namespace boost {
template<class T>
struct use_empty_value_base {
enum {
#if defined(BOOST_DETAIL_EMPTY_VALUE_BASE)
value = __is_empty(T) && !__is_final(T)
#else
value = false
#endif
};
};
struct empty_init_t { };
namespace empty_ {
template<class T, unsigned N = 0,
bool E = boost::use_empty_value_base<T>::value>
class empty_value {
public:
typedef T type;
#if !defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS)
empty_value() = default;
#else
empty_value() { }
#endif
empty_value(boost::empty_init_t)
: value_() { }
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
template<class... Args>
explicit empty_value(boost::empty_init_t, Args&&... args)
: value_(std::forward<Args>(args)...) { }
#else
template<class U>
empty_value(boost::empty_init_t, U&& value)
: value_(std::forward<U>(value)) { }
#endif
#else
template<class U>
empty_value(boost::empty_init_t, const U& value)
: value_(value) { }
#endif
const T& get() const BOOST_NOEXCEPT {
return value_;
}
T& get() BOOST_NOEXCEPT {
return value_;
}
private:
T value_;
};
#if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
template<class T, unsigned N>
class empty_value<T, N, true>
: T {
public:
typedef T type;
#if !defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS)
empty_value() = default;
#else
empty_value() { }
#endif
empty_value(boost::empty_init_t)
: T() { }
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
template<class... Args>
explicit empty_value(boost::empty_init_t, Args&&... args)
: T(std::forward<Args>(args)...) { }
#else
template<class U>
empty_value(boost::empty_init_t, U&& value)
: T(std::forward<U>(value)) { }
#endif
#else
template<class U>
empty_value(boost::empty_init_t, const U& value)
: T(value) { }
#endif
const T& get() const BOOST_NOEXCEPT {
return *this;
}
T& get() BOOST_NOEXCEPT {
return *this;
}
};
#endif
} /* empty_ */
using empty_::empty_value;
} /* boost */
#endif