97 lines
2.9 KiB
C++
97 lines
2.9 KiB
C++
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/*!
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@file
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Adapts `std::integral_constant` for use with Hana.
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@copyright Louis Dionne 2013-2017
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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_EXT_STD_INTEGRAL_CONSTANT_HPP
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#define BOOST_HANA_EXT_STD_INTEGRAL_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/when.hpp>
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#include <boost/hana/fwd/core/to.hpp>
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#include <boost/hana/fwd/core/tag_of.hpp>
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#include <boost/hana/fwd/integral_constant.hpp>
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#include <type_traits>
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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namespace std {
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//! @ingroup group-ext-std
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//! Adapter for `std::integral_constant`s.
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//!
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//! Provided models
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//! ---------------
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//! 1. `Constant` and `IntegralConstant`\n
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//! A `std::integral_constant` is a model of the `IntegralConstant` and
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//! `Constant` concepts, just like `hana::integral_constant`s are. As a
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//! consequence, they are also implicitly a model of the concepts provided
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//! for all models of `Constant`.
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//! @include example/ext/std/integral_constant.cpp
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template <typename T, T v>
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struct integral_constant { };
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}
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#endif
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namespace boost { namespace hana {
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namespace ext { namespace std {
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template <typename T>
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struct integral_constant_tag { using value_type = T; };
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}}
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namespace detail {
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template <typename T, T v>
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constexpr bool
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is_std_integral_constant(std::integral_constant<T, v>*)
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{ return true; }
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constexpr bool is_std_integral_constant(...)
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{ return false; }
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template <typename T, T v>
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constexpr bool
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is_hana_integral_constant(hana::integral_constant<T, v>*)
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{ return true; }
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constexpr bool is_hana_integral_constant(...)
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{ return false; }
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}
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template <typename T>
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struct tag_of<T, when<
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detail::is_std_integral_constant((T*)0) &&
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!detail::is_hana_integral_constant((T*)0)
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>> {
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using type = ext::std::integral_constant_tag<
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typename hana::tag_of<typename T::value_type>::type
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>;
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};
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//////////////////////////////////////////////////////////////////////////
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// Constant/IntegralConstant
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//////////////////////////////////////////////////////////////////////////
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template <typename T>
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struct IntegralConstant<ext::std::integral_constant_tag<T>> {
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static constexpr bool value = true;
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};
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template <typename T, typename C>
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struct to_impl<ext::std::integral_constant_tag<T>, C, when<
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hana::IntegralConstant<C>::value
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>> : embedding<is_embedded<typename C::value_type, T>::value> {
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template <typename N>
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static constexpr auto apply(N const&) {
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return std::integral_constant<T, N::value>{};
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}
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};
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}} // end namespace boost::hana
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#endif // !BOOST_HANA_EXT_STD_INTEGRAL_CONSTANT_HPP
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