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/*!
@file
Defines `boost::hana::detail::index_if`.
@copyright Louis Dionne 2013-2017
@copyright Jason Rice 2017
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_DETAIL_INDEX_IF_HPP
#define BOOST_HANA_DETAIL_INDEX_IF_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/detail/decay.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/optional.hpp>
#include <cstddef>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN namespace detail {
template <std::size_t i, std::size_t N, bool Done>
struct index_if_helper;
template <std::size_t i, std::size_t N>
struct index_if_helper<i, N, false> {
template <typename Pred, typename X1, typename ...Xs>
using f = typename index_if_helper<i + 1, N,
static_cast<bool>(detail::decay<decltype(
std::declval<Pred>()(std::declval<X1>()))>::type::value)
>::template f<Pred, Xs...>;
};
template <std::size_t N>
struct index_if_helper<N, N, false> {
template <typename ...>
using f = hana::optional<>;
};
template <std::size_t i, std::size_t N>
struct index_if_helper<i, N, true> {
template <typename ...>
using f = hana::optional<hana::size_t<i - 1>>;
};
template <typename Pred, typename ...Xs>
struct index_if {
using type = typename index_if_helper<0, sizeof...(Xs), false>
::template f<Pred, Xs...>;
};
} BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_DETAIL_INDEX_IF_HPP
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