| 1 | /*! |
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| 2 | @file |
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| 3 | Forward declares `boost::hana::take_while`. |
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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_TAKE_WHILE_HPP |
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| 11 | #define BOOST_HANA_FWD_TAKE_WHILE_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 | //! Take elements from a sequence while the `predicate` is satisfied. |
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| 19 | //! @ingroup group-Sequence |
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| 20 | //! |
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| 21 | //! Specifically, `take_while` returns a new sequence containing the |
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| 22 | //! longest prefix of `xs` in which all the elements satisfy the given |
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| 23 | //! predicate. |
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| 24 | //! |
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| 25 | //! |
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| 26 | //! @param xs |
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| 27 | //! The sequence to take elements from. |
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| 28 | //! |
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| 29 | //! @param predicate |
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| 30 | //! A function called as `predicate(x)`, where `x` is an element of the |
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| 31 | //! sequence, and returning a `Logical` representing whether `x` should be |
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| 32 | //! included in the resulting sequence. In the current version of the |
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| 33 | //! library, `predicate` has to return a `Constant Logical`. |
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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/take_while.cpp |
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| 39 | #ifdef BOOST_HANA_DOXYGEN_INVOKED |
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| 40 | constexpr auto take_while = [](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 S, typename = void> |
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| 45 | struct take_while_impl : take_while_impl<S, when<true>> { }; |
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| 46 | |
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| 47 | struct take_while_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 take_while_t take_while{}; |
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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_TAKE_WHILE_HPP |
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| 57 | |
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