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/*!
@file
Defines `boost::hana::detail::index_if`.
@copyright Louis Dionne 2013-2017
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/core/when.hpp>
#include <cstddef>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN namespace detail {
template <typename ...T>
struct pack {
static constexpr std::size_t length = sizeof...(T);
};
template <typename T>
struct make_pack;
template <template <typename...> class Template, typename ...T>
struct make_pack<Template<T...>> {
using type = pack<T...>;
};
template <typename T> struct make_pack<T const> : make_pack<T> { };
template <typename T> struct make_pack<T&> : make_pack<T> { };
template <typename T> struct make_pack<T&&> : make_pack<T> { };
//! @ingroup group-details
//! Returns the index of the first element of the `pack<>` that satisfies
//! the predicate, or the size of the pack if there is no such element.
//!
//! @note
//! The predicate must return an `IntegralConstant` that can be explicitly
//! converted to `bool`.
template <typename Pred, typename Ts, typename = when<true>>
struct index_if;
//! @cond
template <typename Pred, typename T, typename ...Ts>
struct index_if<Pred, pack<T, Ts...>, when<static_cast<bool>(decltype(
std::declval<Pred>()(std::declval<T>())
)::value)>> {
static constexpr std::size_t value = 0;
};
template <typename Pred, typename T, typename ...Ts>
struct index_if<Pred, pack<T, Ts...>, when<!static_cast<bool>(decltype(
std::declval<Pred>()(std::declval<T>())
)::value)>> {
static constexpr std::size_t value = 1 + index_if<Pred, pack<Ts...>>::value;
};
template <typename Pred>
struct index_if<Pred, pack<>> {
static constexpr std::size_t value = 0;
};
//! @endcond
} BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_DETAIL_INDEX_IF_HPP
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