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/*!
@file
Forward declares `boost::hana::count_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_FWD_COUNT_IF_HPP
#define BOOST_HANA_FWD_COUNT_IF_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! Return the number of elements in the structure for which the
//! `predicate` is satisfied.
//! @ingroup group-Foldable
//!
//! Specifically, returns an object of an unsigned integral type, or
//! a `Constant` holding such an object, which represents the number
//! of elements in the structure satisfying the given `predicate`.
//!
//!
//! @param xs
//! The structure whose elements are counted.
//!
//! @param predicate
//! A function called as `predicate(x)`, where `x` is an element of the
//! structure, and returning a `Logical` representing whether `x` should
//! be counted.
//!
//!
//! Example
//! -------
//! @include example/count_if.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto count_if = [](auto&& xs, auto&& predicate) {
return tag-dispatched;
};
#else
template <typename T, typename = void>
struct count_if_impl : count_if_impl<T, when<true>> { };
struct count_if_t {
template <typename Xs, typename Pred>
constexpr auto operator()(Xs&& xs, Pred&& pred) const;
};
constexpr count_if_t count_if{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_COUNT_IF_HPP
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