39 lines
943 B
C++
39 lines
943 B
C++
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/*!
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@file
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Defines `boost::hana::id`.
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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_FUNCTIONAL_ID_HPP
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#define BOOST_HANA_FUNCTIONAL_ID_HPP
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#include <boost/hana/config.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @ingroup group-functional
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//! The identity function -- returns its argument unchanged.
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//!
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//! ### Example
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//! @include example/functional/id.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto id = [](auto&& x) -> decltype(auto) {
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return forwarded(x);
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};
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#else
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struct id_t {
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template <typename T>
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constexpr T operator()(T&& t) const {
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return static_cast<T&&>(t);
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}
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};
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constexpr id_t id{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FUNCTIONAL_ID_HPP
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