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 Hu Chunming
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/*!
@file
Defines `boost::hana::detail::array`.
Copyright Louis Dionne 2013-2022
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_DETAIL_ARRAY_HPP
#define BOOST_HANA_DETAIL_ARRAY_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/detail/algorithm.hpp>
#include <boost/hana/functional/placeholder.hpp>
#include <cstddef>
namespace boost { namespace hana { namespace detail {
template <typename N>
constexpr N factorial(N n) {
N result = 1;
while (n != 0)
result *= n--;
return result;
}
//! @ingroup group-details
//! A minimal `std::array` with better `constexpr` support.
//!
//! We also provide some algorithms from the `constexpr/algorithm.hpp`
//! header as member functions to make them easier to use in constexpr
//! contexts, since a `constexpr` `array` can't be mutated in place.
template <typename T, std::size_t Size>
struct array {
T elems_[Size > 0 ? Size : 1];
constexpr T& operator[](std::size_t n)
{ return elems_[n]; }
constexpr T const& operator[](std::size_t n) const
{ return elems_[n]; }
constexpr std::size_t size() const noexcept
{ return Size; }
constexpr T* begin() noexcept { return elems_; }
constexpr T const* begin() const noexcept { return elems_; }
constexpr T* end() noexcept { return elems_ + Size; }
constexpr T const* end() const noexcept { return elems_ + Size; }
// Algorithms from constexpr/algorithm.hpp
constexpr array reverse() const {
array result = *this;
detail::reverse(result.begin(), result.end());
return result;
}
template <typename BinaryPred>
constexpr auto permutations(BinaryPred pred) const {
array<array<T, Size>, detail::factorial(Size)> result{};
auto out = result.begin();
array copy = *this;
do *out++ = copy;
while (detail::next_permutation(copy.begin(), copy.end(), pred));
return result;
}
constexpr auto permutations() const
{ return this->permutations(hana::_ < hana::_); }
template <typename BinaryPred>
constexpr auto sort(BinaryPred pred) const {
array result = *this;
detail::sort(result.begin(), result.end(), pred);
return result;
}
constexpr auto sort() const
{ return this->sort(hana::_ < hana::_); }
template <typename U>
constexpr auto iota(U value) const {
array result = *this;
detail::iota(result.begin(), result.end(), value);
return result;
}
};
template <typename T, std::size_t M, typename U, std::size_t N>
constexpr bool operator==(array<T, M> a, array<U, N> b)
{ return M == N && detail::equal(a.begin(), a.end(), b.begin(), b.end()); }
template <typename T, std::size_t M, typename U, std::size_t N>
constexpr bool operator<(array<T, M> a, array<U, N> b) {
return M < N || detail::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end());
}
} }} // end namespace boost::hana
#endif // !BOOST_HANA_DETAIL_ARRAY_HPP
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