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