boost/hana/duplicate.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::duplicate`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_DUPLICATE_HPP
0011 #define BOOST_HANA_DUPLICATE_HPP
0012
0013 #include <boost/hana/fwd/duplicate.hpp>
0014
0015 #include <boost/hana/concept/comonad.hpp>
0016 #include <boost/hana/config.hpp>
0017 #include <boost/hana/core/dispatch.hpp>
0018 #include <boost/hana/extend.hpp>
0019 #include <boost/hana/functional/id.hpp>
0020
0021
0022 namespace boost { namespace hana {
0023     //! @cond
0024     template <typename W_>
0025     constexpr decltype(auto) duplicate_t::operator()(W_&& w) const {
0026         using W = typename hana::tag_of<W_>::type;
0027         using Duplicate = BOOST_HANA_DISPATCH_IF(duplicate_impl<W>,
0028             hana::Comonad<W>::value
0029         );
0030
0031     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0032         static_assert(hana::Comonad<W>::value,
0033         "hana::duplicate(w) requires 'w' to be a Comonad");
0034     #endif
0035
0036         return Duplicate::apply(static_cast<W_&&>(w));
0037     }
0038     //! @endcond
0039
0040     template <typename W, bool condition>
0041     struct duplicate_impl<W, when<condition>> : default_ {
0042         template <typename X>
0043         static constexpr decltype(auto) apply(X&& x)
0044         { return hana::extend(static_cast<X&&>(x), hana::id); }
0045     };
0046 }} // end namespace boost::hana
0047
0048 #endif // !BOOST_HANA_DUPLICATE_HPP