57 lines
1.7 KiB
C++
57 lines
1.7 KiB
C++
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/*!
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@file
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Forward declares `boost::hana::count_if`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_FWD_COUNT_IF_HPP
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#define BOOST_HANA_FWD_COUNT_IF_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/when.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! Return the number of elements in the structure for which the
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//! `predicate` is satisfied.
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//! @ingroup group-Foldable
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//!
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//! Specifically, returns an object of an unsigned integral type, or
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//! a `Constant` holding such an object, which represents the number
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//! of elements in the structure satisfying the given `predicate`.
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//!
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//!
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//! @param xs
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//! The structure whose elements are counted.
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//!
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//! @param predicate
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//! A function called as `predicate(x)`, where `x` is an element of the
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//! structure, and returning a `Logical` representing whether `x` should
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//! be counted.
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//!
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//!
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//! Example
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//! -------
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//! @include example/count_if.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto count_if = [](auto&& xs, auto&& predicate) {
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return tag-dispatched;
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};
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#else
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template <typename T, typename = void>
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struct count_if_impl : count_if_impl<T, when<true>> { };
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struct count_if_t {
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template <typename Xs, typename Pred>
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constexpr auto operator()(Xs&& xs, Pred&& pred) const;
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};
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constexpr count_if_t count_if{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_COUNT_IF_HPP
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