1 /*! 2 @file 3 Defines `boost::hana::intersperse`. 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_INTERSPERSE_HPP 11 #define BOOST_HANA_INTERSPERSE_HPP 12 13 #include <boost/hana/fwd/intersperse.hpp> 14 15 #include <boost/hana/at.hpp> 16 #include <boost/hana/bool.hpp> 17 #include <boost/hana/concept/sequence.hpp> 18 #include <boost/hana/config.hpp> 19 #include <boost/hana/core/dispatch.hpp> 20 #include <boost/hana/core/make.hpp> 21 #include <boost/hana/length.hpp> 22 23 #include <cstddef> 24 #include <utility> 25 26 27 BOOST_HANA_NAMESPACE_BEGIN 28 //! @cond 29 template <typename Xs, typename Z> operator ()(Xs && xs,Z && z) const30 constexpr auto intersperse_t::operator()(Xs&& xs, Z&& z) const { 31 using S = typename hana::tag_of<Xs>::type; 32 using Intersperse = BOOST_HANA_DISPATCH_IF(intersperse_impl<S>, 33 hana::Sequence<S>::value 34 ); 35 36 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS 37 static_assert(hana::Sequence<S>::value, 38 "hana::intersperse(xs, z) requires 'xs' to be a Sequence"); 39 #endif 40 41 return Intersperse::apply(static_cast<Xs&&>(xs), static_cast<Z&&>(z)); 42 } 43 //! @endcond 44 45 template <typename S, bool condition> 46 struct intersperse_impl<S, when<condition>> : default_ { 47 template <std::size_t i, typename Xs, typename Z> 48 static constexpr decltype(auto) pickintersperse_impl49 pick(Xs&&, Z&& z, hana::false_ /* odd index */) 50 { return static_cast<Z&&>(z); } 51 52 template <std::size_t i, typename Xs, typename Z> 53 static constexpr decltype(auto) pickintersperse_impl54 pick(Xs&& xs, Z&&, hana::true_ /* even index */) 55 { return hana::at_c<(i + 1) / 2>(static_cast<Xs&&>(xs)); } 56 57 template <typename Xs, typename Z, std::size_t ...i> 58 static constexpr auto intersperse_helperintersperse_impl59 intersperse_helper(Xs&& xs, Z&& z, std::index_sequence<i...>) { 60 return hana::make<S>( 61 pick<i>(static_cast<Xs&&>(xs), static_cast<Z&&>(z), 62 hana::bool_c<(i % 2 == 0)>)... 63 ); 64 } 65 66 template <typename Xs, typename Z> applyintersperse_impl67 static constexpr auto apply(Xs&& xs, Z&& z) { 68 constexpr std::size_t size = decltype(hana::length(xs))::value; 69 constexpr std::size_t new_size = size == 0 ? 0 : (size * 2) - 1; 70 return intersperse_helper(static_cast<Xs&&>(xs), static_cast<Z&&>(z), 71 std::make_index_sequence<new_size>{}); 72 } 73 }; 74 BOOST_HANA_NAMESPACE_END 75 76 #endif // !BOOST_HANA_INTERSPERSE_HPP 77