/*! @file Defines `boost::hana::duplicate`. @copyright Louis Dionne 2013-2017 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