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