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1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::permutations`. | |
4 | ||
5 | @copyright Louis Dionne 2013-2016 | |
6 | Distributed under the Boost Software License, Version 1.0. | |
7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
8 | */ | |
9 | ||
10 | #ifndef BOOST_HANA_FWD_PERMUTATIONS_HPP | |
11 | #define BOOST_HANA_FWD_PERMUTATIONS_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | #include <boost/hana/core/when.hpp> | |
15 | ||
16 | ||
17 | BOOST_HANA_NAMESPACE_BEGIN | |
18 | //! Return a sequence of all the permutations of the given sequence. | |
19 | //! @ingroup group-Sequence | |
20 | //! | |
21 | //! Specifically, `permutations(xs)` is a sequence whose elements are | |
22 | //! permutations of the original sequence `xs`. The permutations are not | |
23 | //! guaranteed to be in any specific order. Also note that the number | |
24 | //! of permutations grows very rapidly as the length of the original | |
25 | //! sequence increases. The growth rate is `O(length(xs)!)`; with a | |
26 | //! sequence `xs` of length only 8, `permutations(xs)` contains over | |
27 | //! 40 000 elements! | |
28 | //! | |
29 | //! | |
30 | //! Example | |
31 | //! ------- | |
32 | //! @include example/permutations.cpp | |
33 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
34 | constexpr auto permutations = [](auto&& xs) { | |
35 | return tag-dispatched; | |
36 | }; | |
37 | #else | |
38 | template <typename S, typename = void> | |
39 | struct permutations_impl : permutations_impl<S, when<true>> { }; | |
40 | ||
41 | struct permutations_t { | |
42 | template <typename Xs> | |
43 | constexpr auto operator()(Xs&& xs) const; | |
44 | }; | |
45 | ||
46 | constexpr permutations_t permutations{}; | |
47 | #endif | |
48 | BOOST_HANA_NAMESPACE_END | |
49 | ||
50 | #endif // !BOOST_HANA_FWD_PERMUTATIONS_HPP |