1 /*! 2 @file 3 Defines `boost::hana::duplicate`. 4 5 @copyright Louis Dionne 2013-2017 6 Distributed under the Boost Software License, Version 1.0. 7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) 8 */ 9 10 #ifndef BOOST_HANA_DUPLICATE_HPP 11 #define BOOST_HANA_DUPLICATE_HPP 12 13 #include <boost/hana/fwd/duplicate.hpp> 14 15 #include <boost/hana/concept/comonad.hpp> 16 #include <boost/hana/config.hpp> 17 #include <boost/hana/core/dispatch.hpp> 18 #include <boost/hana/extend.hpp> 19 #include <boost/hana/functional/id.hpp> 20 21 22 BOOST_HANA_NAMESPACE_BEGIN 23 //! @cond 24 template <typename W_> operator ()(W_ && w) const25 constexpr decltype(auto) duplicate_t::operator()(W_&& w) const { 26 using W = typename hana::tag_of<W_>::type; 27 using Duplicate = BOOST_HANA_DISPATCH_IF(duplicate_impl<W>, 28 hana::Comonad<W>::value 29 ); 30 31 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS 32 static_assert(hana::Comonad<W>::value, 33 "hana::duplicate(w) requires 'w' to be a Comonad"); 34 #endif 35 36 return Duplicate::apply(static_cast<W_&&>(w)); 37 } 38 //! @endcond 39 40 template <typename W, bool condition> 41 struct duplicate_impl<W, when<condition>> : default_ { 42 template <typename X> applyduplicate_impl43 static constexpr decltype(auto) apply(X&& x) 44 { return hana::extend(static_cast<X&&>(x), hana::id); } 45 }; 46 BOOST_HANA_NAMESPACE_END 47 48 #endif // !BOOST_HANA_DUPLICATE_HPP 49