1 /*! 2 @file 3 Defines `boost::hana::Foldable`. 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_CONCEPT_FOLDABLE_HPP 11 #define BOOST_HANA_CONCEPT_FOLDABLE_HPP 12 13 #include <boost/hana/fwd/concept/foldable.hpp> 14 15 #include <boost/hana/config.hpp> 16 #include <boost/hana/core/default.hpp> 17 #include <boost/hana/core/tag_of.hpp> 18 #include <boost/hana/detail/integral_constant.hpp> 19 #include <boost/hana/fold_left.hpp> 20 #include <boost/hana/unpack.hpp> 21 22 23 BOOST_HANA_NAMESPACE_BEGIN 24 template <typename T> 25 struct Foldable 26 : hana::integral_constant<bool, 27 !is_default<fold_left_impl<typename tag_of<T>::type>>::value || 28 !is_default<unpack_impl<typename tag_of<T>::type>>::value 29 > 30 { }; 31 BOOST_HANA_NAMESPACE_END 32 33 #endif // !BOOST_HANA_CONCEPT_FOLDABLE_HPP 34