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/*!
@file
Adapts `std::array` for use with Hana.
@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_EXT_STD_ARRAY_HPP
#define BOOST_HANA_EXT_STD_ARRAY_HPP
#include <boost/hana/bool.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/detail/algorithm.hpp>
#include <boost/hana/fwd/at.hpp>
#include <boost/hana/fwd/core/tag_of.hpp>
#include <boost/hana/fwd/drop_front.hpp>
#include <boost/hana/fwd/equal.hpp>
#include <boost/hana/fwd/is_empty.hpp>
#include <boost/hana/fwd/length.hpp>
#include <boost/hana/fwd/less.hpp>
#include <boost/hana/integral_constant.hpp>
#include <array>
#include <cstddef>
#include <type_traits>
#include <utility>
#ifdef BOOST_HANA_DOXYGEN_INVOKED
namespace std {
//! @ingroup group-ext-std
//! Adaptation of `std::array` for Hana.
//!
//!
//!
//! Modeled concepts
//! ----------------
//! 1. `Comparable`\n
//! `std::array`s are compared as per `std::equal`, except that two arrays
//! with different sizes compare unequal instead of triggering an error
//! and the result of the comparison is `constexpr` if both arrays are
//! `constexpr`.
//! @include example/ext/std/array/comparable.cpp
//!
//! 2. `Orderable`\n
//! `std::array`s are ordered with the usual lexicographical ordering,
//! except that two arrays with different size can be ordered instead
//! of triggering an error and the result of the comparison is `constexpr`
//! if both arrays are `constexpr`.
//! @include example/ext/std/array/orderable.cpp
//!
//! 3. `Foldable`\n
//! Folding an array from the left is equivalent to calling
//! `std::accumulate` on it, except it can be `constexpr`.
//! @include example/ext/std/array/foldable.cpp
//!
//! 4. `Iterable`\n
//! Iterating over a `std::array` is equivalent to iterating over it with
//! a normal `for` loop.
//! @include example/ext/std/array/iterable.cpp
template <typename T, std::size_t N>
struct array { };
}
#endif
BOOST_HANA_NAMESPACE_BEGIN
namespace ext { namespace std { struct array_tag; }}
template <typename T, std::size_t N>
struct tag_of<std::array<T, N>> {
using type = ext::std::array_tag;
};
//////////////////////////////////////////////////////////////////////////
// Foldable
//////////////////////////////////////////////////////////////////////////
template <>
struct length_impl<ext::std::array_tag> {
template <typename Xs>
static constexpr auto apply(Xs const&) {
return hana::size_c<std::tuple_size<Xs>::type::value>;
}
};
//////////////////////////////////////////////////////////////////////////
// Iterable
//////////////////////////////////////////////////////////////////////////
template <>
struct at_impl<ext::std::array_tag> {
template <typename Xs, typename N>
static constexpr decltype(auto) apply(Xs&& xs, N const&) {
constexpr std::size_t n = N::value;
return std::get<n>(static_cast<Xs&&>(xs));
}
};
template <>
struct drop_front_impl<ext::std::array_tag> {
template <std::size_t n, typename Xs, std::size_t ...i>
static constexpr auto drop_front_helper(Xs&& xs, std::index_sequence<i...>) {
using T = typename std::remove_reference<Xs>::type::value_type;
return std::array<T, sizeof...(i)>{{static_cast<Xs&&>(xs)[n + i]...}};
}
template <typename Xs, typename N>
static constexpr auto apply(Xs&& xs, N const&) {
constexpr std::size_t n = N::value;
constexpr std::size_t len = std::tuple_size<
typename std::remove_cv<
typename std::remove_reference<Xs>::type
>::type
>::value;
return drop_front_helper<n>(static_cast<Xs&&>(xs),
std::make_index_sequence<(n < len ? len - n : 0)>{});
}
};
template <>
struct is_empty_impl<ext::std::array_tag> {
template <typename T, std::size_t N>
static constexpr auto apply(std::array<T, N> const&) {
return hana::bool_c<N == 0>;
}
};
//////////////////////////////////////////////////////////////////////////
// Comparable
//////////////////////////////////////////////////////////////////////////
template <>
struct equal_impl<ext::std::array_tag, ext::std::array_tag> {
template <typename T, std::size_t n, typename U>
static constexpr bool apply(std::array<T, n> const& xs, std::array<U, n> const& ys)
{ return detail::equal(&xs[0], &xs[0] + n, &ys[0], &ys[0] + n); }
template <typename T, typename U>
static constexpr auto apply(std::array<T, 0> const&, std::array<U, 0> const&)
{ return hana::true_c; }
template <typename T, std::size_t n, typename U, std::size_t m>
static constexpr auto apply(std::array<T, n> const&, std::array<U, m> const&)
{ return hana::false_c; }
};
//////////////////////////////////////////////////////////////////////////
// Orderable
//////////////////////////////////////////////////////////////////////////
template <>
struct less_impl<ext::std::array_tag, ext::std::array_tag> {
template <typename T, typename U>
static constexpr auto apply(std::array<T, 0> const&, std::array<U, 0> const&)
{ return hana::false_c; }
template <typename T, std::size_t n, typename U, std::size_t m>
static constexpr auto apply(std::array<T, n> const& xs, std::array<U, m> const& ys) {
return detail::lexicographical_compare(&xs[0], &xs[0] + n, &ys[0], &ys[0] + m);
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_EXT_STD_ARRAY_HPP
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