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Diffstat (limited to 'boost/hana/duplicate.hpp')
-rw-r--r-- | boost/hana/duplicate.hpp | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/boost/hana/duplicate.hpp b/boost/hana/duplicate.hpp new file mode 100644 index 0000000000..1df6fb7a85 --- /dev/null +++ b/boost/hana/duplicate.hpp @@ -0,0 +1,48 @@ +/*! +@file +Defines `boost::hana::duplicate`. + +@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_DUPLICATE_HPP +#define BOOST_HANA_DUPLICATE_HPP + +#include <boost/hana/fwd/duplicate.hpp> + +#include <boost/hana/concept/comonad.hpp> +#include <boost/hana/config.hpp> +#include <boost/hana/core/dispatch.hpp> +#include <boost/hana/extend.hpp> +#include <boost/hana/functional/id.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! @cond + template <typename W_> + constexpr decltype(auto) duplicate_t::operator()(W_&& w) const { + using W = typename hana::tag_of<W_>::type; + using Duplicate = BOOST_HANA_DISPATCH_IF(duplicate_impl<W>, + hana::Comonad<W>::value + ); + + #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS + static_assert(hana::Comonad<W>::value, + "hana::duplicate(w) requires 'w' to be a Comonad"); + #endif + + return Duplicate::apply(static_cast<W_&&>(w)); + } + //! @endcond + + template <typename W, bool condition> + struct duplicate_impl<W, when<condition>> : default_ { + template <typename X> + static constexpr decltype(auto) apply(X&& x) + { return hana::extend(static_cast<X&&>(x), hana::id); } + }; +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_DUPLICATE_HPP |