1 /*!
2 @file
3 Defines `boost::hana::Foldable`.
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_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