51 lines
1.6 KiB
C++
51 lines
1.6 KiB
C++
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/*!
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@file
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Forward declares `boost::hana::permutations`.
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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_PERMUTATIONS_HPP
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#define BOOST_HANA_FWD_PERMUTATIONS_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 a sequence of all the permutations of the given sequence.
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//! @ingroup group-Sequence
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//!
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//! Specifically, `permutations(xs)` is a sequence whose elements are
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//! permutations of the original sequence `xs`. The permutations are not
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//! guaranteed to be in any specific order. Also note that the number
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//! of permutations grows very rapidly as the length of the original
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//! sequence increases. The growth rate is `O(length(xs)!)`; with a
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//! sequence `xs` of length only 8, `permutations(xs)` contains over
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//! 40 000 elements!
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//!
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//!
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//! Example
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//! -------
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//! @include example/permutations.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto permutations = [](auto&& xs) {
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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 permutations_impl : permutations_impl<S, when<true>> { };
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struct permutations_t {
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template <typename Xs>
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constexpr auto operator()(Xs&& xs) const;
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};
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constexpr permutations_t permutations{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_PERMUTATIONS_HPP
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