| 1 | /*! |
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| 2 | @file |
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| 3 | Forward declares `boost::hana::count_if`. |
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| 4 | |
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| 5 | Copyright Louis Dionne 2013-2022 |
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| 6 | Distributed under the Boost Software License, Version 1.0. |
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| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
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| 8 | */ |
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| 9 | |
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| 10 | #ifndef BOOST_HANA_FWD_COUNT_IF_HPP |
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| 11 | #define BOOST_HANA_FWD_COUNT_IF_HPP |
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| 12 | |
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| 13 | #include <boost/hana/config.hpp> |
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| 14 | #include <boost/hana/core/when.hpp> |
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| 15 | |
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| 16 | |
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| 17 | namespace boost { namespace hana { |
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| 18 | //! Return the number of elements in the structure for which the |
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| 19 | //! `predicate` is satisfied. |
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| 20 | //! @ingroup group-Foldable |
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| 21 | //! |
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| 22 | //! Specifically, returns an object of an unsigned integral type, or |
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| 23 | //! a `Constant` holding such an object, which represents the number |
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| 24 | //! of elements in the structure satisfying the given `predicate`. |
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| 25 | //! |
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| 26 | //! |
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| 27 | //! @param xs |
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| 28 | //! The structure whose elements are counted. |
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| 29 | //! |
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| 30 | //! @param predicate |
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| 31 | //! A function called as `predicate(x)`, where `x` is an element of the |
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| 32 | //! structure, and returning a `Logical` representing whether `x` should |
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| 33 | //! be counted. |
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| 34 | //! |
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| 35 | //! |
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| 36 | //! Example |
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| 37 | //! ------- |
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| 38 | //! @include example/count_if.cpp |
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| 39 | #ifdef BOOST_HANA_DOXYGEN_INVOKED |
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| 40 | constexpr auto count_if = [](auto&& xs, auto&& predicate) { |
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| 41 | return tag-dispatched; |
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| 42 | }; |
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| 43 | #else |
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| 44 | template <typename T, typename = void> |
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| 45 | struct count_if_impl : count_if_impl<T, when<true>> { }; |
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| 46 | |
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| 47 | struct count_if_t { |
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| 48 | template <typename Xs, typename Pred> |
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| 49 | constexpr auto operator()(Xs&& xs, Pred&& pred) const; |
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| 50 | }; |
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| 51 | |
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| 52 | BOOST_HANA_INLINE_VARIABLE constexpr count_if_t count_if{}; |
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| 53 | #endif |
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| 54 | }} // end namespace boost::hana |
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| 55 | |
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| 56 | #endif // !BOOST_HANA_FWD_COUNT_IF_HPP |
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| 57 | |
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