58 lines
1.7 KiB
C++
58 lines
1.7 KiB
C++
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/*!
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@file
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Forward declares `boost::hana::find_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_FIND_IF_HPP
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#define BOOST_HANA_FWD_FIND_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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//! Finds the value associated to the first key satisfying a predicate.
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//! @ingroup group-Searchable
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//!
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//! Given a `Searchable` structure `xs` and a predicate `pred`,
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//! `find_if(xs, pred)` returns `just` the first element whose key
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//! satisfies the predicate, or `nothing` if there is no such element.
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//!
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//!
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//! @param xs
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//! The structure to be searched.
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//!
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//! @param predicate
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//! A function called as `predicate(k)`, where `k` is a key of the
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//! structure, and returning whether `k` is the key of the element
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//! being searched for. In the current version of the library, the
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//! predicate has to return an `IntegralConstant` holding a value
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//! that can be converted to `bool`.
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//!
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//!
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//! Example
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//! -------
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//! @include example/find_if.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto find_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 S, typename = void>
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struct find_if_impl : find_if_impl<S, when<true>> { };
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struct find_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 find_if_t find_if{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_FIND_IF_HPP
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