57 lines
1.6 KiB
C++
57 lines
1.6 KiB
C++
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/*!
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@file
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Defines `boost::hana::value`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_VALUE_HPP
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#define BOOST_HANA_VALUE_HPP
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#include <boost/hana/fwd/value.hpp>
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#include <boost/hana/concept/constant.hpp>
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#include <boost/hana/concept/integral_constant.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <type_traits>
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BOOST_HANA_NAMESPACE_BEGIN
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template <typename C, bool condition>
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struct value_impl<C, when<condition>> : default_ {
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template <typename ...Args>
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static constexpr auto apply(Args&& ...args) = delete;
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};
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template <typename T>
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constexpr decltype(auto) value() {
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using RawT = typename std::remove_cv<
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typename std::remove_reference<T>::type
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>::type;
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using C = typename hana::tag_of<RawT>::type;
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using Value = BOOST_HANA_DISPATCH_IF(
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value_impl<C>, hana::Constant<C>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Constant<C>::value,
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"hana::value<T>() requires 'T' to be a Constant");
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#endif
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return Value::template apply<RawT>();
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}
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template <typename I>
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struct value_impl<I, when<hana::IntegralConstant<I>::value>> {
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template <typename C>
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static constexpr auto apply()
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{ return C::value; }
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_VALUE_HPP
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