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Diffstat (limited to 'boost/hana/functional/id.hpp')
-rw-r--r-- | boost/hana/functional/id.hpp | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/boost/hana/functional/id.hpp b/boost/hana/functional/id.hpp new file mode 100644 index 0000000000..e6b4e32b79 --- /dev/null +++ b/boost/hana/functional/id.hpp @@ -0,0 +1,38 @@ +/*! +@file +Defines `boost::hana::id`. + +@copyright Louis Dionne 2013-2016 +Distributed under the Boost Software License, Version 1.0. +(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) + */ + +#ifndef BOOST_HANA_FUNCTIONAL_ID_HPP +#define BOOST_HANA_FUNCTIONAL_ID_HPP + +#include <boost/hana/config.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! @ingroup group-functional + //! The identity function -- returns its argument unchanged. + //! + //! ### Example + //! @include example/functional/id.cpp +#ifdef BOOST_HANA_DOXYGEN_INVOKED + constexpr auto id = [](auto&& x) -> decltype(auto) { + return forwarded(x); + }; +#else + struct id_t { + template <typename T> + constexpr T operator()(T&& t) const { + return static_cast<T&&>(t); + } + }; + + constexpr id_t id{}; +#endif +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_FUNCTIONAL_ID_HPP |