141 lines
5.2 KiB
C++
141 lines
5.2 KiB
C++
/*!
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@file
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Adapts `std::integer_sequence` for use with Hana.
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@copyright Louis Dionne 2013-2017
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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_EXT_STD_INTEGER_SEQUENCE_HPP
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#define BOOST_HANA_EXT_STD_INTEGER_SEQUENCE_HPP
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#include <boost/hana/bool.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/detail/fast_and.hpp>
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#include <boost/hana/ext/std/integral_constant.hpp>
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#include <boost/hana/fwd/at.hpp>
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#include <boost/hana/fwd/core/tag_of.hpp>
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#include <boost/hana/fwd/drop_front.hpp>
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#include <boost/hana/fwd/equal.hpp>
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#include <boost/hana/fwd/is_empty.hpp>
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#include <boost/hana/fwd/unpack.hpp>
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#include <cstddef>
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#include <type_traits>
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#include <utility>
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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namespace std {
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//! @ingroup group-ext-std
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//! Adaptation of `std::integer_sequence` for Hana.
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//!
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//!
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//!
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//! Modeled concepts
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//! ----------------
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//! 1. `Comparable`\n
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//! Two `std::integer_sequence`s are equal if and only if they have the
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//! same number of elements, and if corresponding elements compare equal.
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//! The types of the elements held in both `integer_sequence`s may be
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//! different, as long as they can be compared.
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//! @include example/ext/std/integer_sequence/comparable.cpp
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//!
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//! 2. `Foldable`\n
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//! Folding an `integer_sequence` is equivalent to folding a sequence of
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//! `std::integral_constant`s with the corresponding types.
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//! @include example/ext/std/integer_sequence/foldable.cpp
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//!
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//! 3. `Iterable`\n
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//! Iterating over an `integer_sequence` is equivalent to iterating over
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//! a sequence of the corresponding `std::integral_constant`s.
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//! @include example/ext/std/integer_sequence/iterable.cpp
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//!
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//! 4. `Searchable`\n
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//! Searching through an `integer_sequence` is equivalent to searching
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//! through the corresponding sequence of `std::integral_constant`s.
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//! @include example/ext/std/integer_sequence/searchable.cpp
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template <typename T, T ...v>
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struct integer_sequence { };
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}
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#endif
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namespace boost { namespace hana {
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namespace ext { namespace std { struct integer_sequence_tag; }}
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template <typename T, T ...v>
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struct tag_of<std::integer_sequence<T, v...>> {
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using type = ext::std::integer_sequence_tag;
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};
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//////////////////////////////////////////////////////////////////////////
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// Comparable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct equal_impl<ext::std::integer_sequence_tag, ext::std::integer_sequence_tag> {
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template <typename X, X ...xs, typename Y, Y ...ys>
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static constexpr hana::bool_<detail::fast_and<(xs == ys)...>::value>
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apply(std::integer_sequence<X, xs...> const&, std::integer_sequence<Y, ys...> const&)
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{ return {}; }
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template <typename Xs, typename Ys>
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static constexpr hana::false_ apply(Xs const&, Ys const&, ...)
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{ return {}; }
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};
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//////////////////////////////////////////////////////////////////////////
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// Foldable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct unpack_impl<ext::std::integer_sequence_tag> {
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template <typename T, T ...v, typename F>
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static constexpr decltype(auto)
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apply(std::integer_sequence<T, v...> const&, F&& f) {
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return static_cast<F&&>(f)(std::integral_constant<T, v>{}...);
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// Iterable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct at_impl<ext::std::integer_sequence_tag> {
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template <typename T, T ...v, typename N>
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static constexpr auto apply(std::integer_sequence<T, v...> const&, N const&) {
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constexpr std::size_t n = N::value;
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constexpr T values_[] = {v...};
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return std::integral_constant<T, values_[n]>{};
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}
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};
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template <>
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struct drop_front_impl<ext::std::integer_sequence_tag> {
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template <std::size_t n, typename T, T ...t, std::size_t ...i>
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static constexpr auto drop_front_helper(std::integer_sequence<T, t...>,
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std::index_sequence<i...>)
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{
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constexpr T ts[sizeof...(t)+1] = {t...}; // avoid 0-sized array
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return std::integer_sequence<T, ts[n + i]...>{};
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}
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template <typename T, T ...t, typename N>
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static constexpr auto apply(std::integer_sequence<T, t...> ts, N const&) {
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constexpr std::size_t n = N::value;
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constexpr std::size_t len = sizeof...(t);
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return drop_front_helper<n>(ts,
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std::make_index_sequence<(n < len ? len - n : 0)>{});
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}
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};
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template <>
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struct is_empty_impl<ext::std::integer_sequence_tag> {
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template <typename T, T ...xs>
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static constexpr auto apply(std::integer_sequence<T, xs...> const&)
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{ return hana::bool_c<sizeof...(xs) == 0>; }
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};
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}} // end namespace boost::hana
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#endif // !BOOST_HANA_EXT_STD_INTEGER_SEQUENCE_HPP
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