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 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 ``` ``````/*! @file Forward declares `boost::hana::count`. @copyright Louis Dionne 2013-2016 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_HPP #define BOOST_HANA_FWD_COUNT_HPP #include #include BOOST_HANA_NAMESPACE_BEGIN //! Return the number of elements in the structure that compare equal to //! a given value. //! @ingroup group-Foldable //! //! Given a Foldable structure `xs` and a value `value`, `count` returns //! an unsigned integral, or a Constant thereof, representing the number //! of elements of `xs` that compare equal to `value`. For this method to //! be well-defined, all the elements of the structure must be Comparable //! with the given value. //! //! //! @param xs //! The structure whose elements are counted. //! //! @param value //! A value compared with each element in the structure. Elements //! that compare equal to this value are counted, others are not. //! //! //! Example //! ------- //! @include example/count.cpp #ifdef BOOST_HANA_DOXYGEN_INVOKED constexpr auto count = [](auto&& xs, auto&& value) { return tag-dispatched; }; #else template struct count_impl : count_impl> { }; struct count_t { template constexpr auto operator()(Xs&& xs, Value&& value) const; }; constexpr count_t count{}; #endif BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_FWD_COUNT_HPP ``````