1 /*!
2 @file
3 Defines `boost::hana::detail::first_unsatisfied_index`.
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_DETAIL_FIRST_UNSATISFIED_INDEX_HPP
11 #define BOOST_HANA_DETAIL_FIRST_UNSATISFIED_INDEX_HPP
12 
13 #include <boost/hana/config.hpp>
14 #include <boost/hana/integral_constant.hpp>
15 #include <boost/hana/value.hpp>
16 
17 #include <utility>
18 
19 
20 BOOST_HANA_NAMESPACE_BEGIN namespace detail {
21     template <bool, typename Pred, typename ...Xs>
22     struct find_tail_size;
23 
24     template <typename Pred, typename X, typename ...Xs>
25     struct find_tail_size<true, Pred, X, Xs...> {
26         static constexpr int value = find_tail_size<
27             static_cast<bool>(hana::value<decltype(std::declval<Pred>()(std::declval<X>()))>()),
28             Pred, Xs...
29         >::value;
30     };
31 
32     template <typename Pred>
33     struct find_tail_size<true, Pred> {
34         static constexpr int value = -1;
35     };
36 
37     template <typename Pred, typename ...Xs>
38     struct find_tail_size<false, Pred, Xs...> {
39         static constexpr int value = sizeof...(Xs);
40     };
41 
42     //! @ingroup group-details
43     //! Returns the index of the first element which does not satisfy `Pred`,
44     //! or `sizeof...(Xs)` if no such element exists.
45     template <typename Pred>
46     struct first_unsatisfied_index {
47         template <typename ...Xs>
operator ()detail::first_unsatisfied_index48         constexpr auto operator()(Xs&& ...) const {
49             return hana::size_c<
50                 sizeof...(Xs) - 1 - find_tail_size<true, Pred, Xs&&...>::value
51             >;
52         }
53     };
54 } BOOST_HANA_NAMESPACE_END
55 
56 #endif // !BOOST_HANA_DETAIL_FIRST_UNSATISFIED_INDEX_HPP
57