1 /*! 2 @file 3 Defines `boost::hana::product`. 4 5 @copyright Louis Dionne 2013-2016 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_PRODUCT_HPP 11 #define BOOST_HANA_PRODUCT_HPP 12 13 #include <boost/hana/fwd/product.hpp> 14 15 #include <boost/hana/concept/foldable.hpp> 16 #include <boost/hana/concept/ring.hpp> 17 #include <boost/hana/config.hpp> 18 #include <boost/hana/core/dispatch.hpp> 19 #include <boost/hana/fold_left.hpp> 20 #include <boost/hana/integral_constant.hpp> // required by fwd decl 21 #include <boost/hana/mult.hpp> 22 #include <boost/hana/one.hpp> 23 24 25 BOOST_HANA_NAMESPACE_BEGIN 26 template <typename R> 27 struct product_t { 28 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS 29 static_assert(hana::Ring<R>::value, 30 "hana::product<R> requires 'R' to be a Ring"); 31 #endif 32 33 template <typename Xs> operator ()product_t34 constexpr decltype(auto) operator()(Xs&& xs) const { 35 using S = typename hana::tag_of<Xs>::type; 36 using Product = BOOST_HANA_DISPATCH_IF(product_impl<S>, 37 hana::Foldable<S>::value 38 ); 39 40 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS 41 static_assert(hana::Foldable<S>::value, 42 "hana::product<R>(xs) requires 'xs' to be Foldable"); 43 #endif 44 45 return Product::template apply<R>(static_cast<Xs&&>(xs)); 46 } 47 }; 48 49 template <typename T, bool condition> 50 struct product_impl<T, when<condition>> : default_ { 51 template <typename R, typename Xs> applyproduct_impl52 static constexpr decltype(auto) apply(Xs&& xs) { 53 return hana::fold_left(static_cast<Xs&&>(xs), hana::one<R>(), hana::mult); 54 } 55 }; 56 BOOST_HANA_NAMESPACE_END 57 58 #endif // !BOOST_HANA_PRODUCT_HPP 59