86 lines
3.0 KiB
C++
86 lines
3.0 KiB
C++
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/*!
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@file
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Defines `boost::hana::drop_front_exactly`.
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@copyright Louis Dionne 2013-2016
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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_DROP_FRONT_EXACTLY_HPP
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#define BOOST_HANA_DROP_FRONT_EXACTLY_HPP
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#include <boost/hana/fwd/drop_front_exactly.hpp>
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#include <boost/hana/bool.hpp>
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#include <boost/hana/concept/integral_constant.hpp>
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#include <boost/hana/concept/iterable.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/drop_front.hpp>
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#include <boost/hana/integral_constant.hpp>
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#include <boost/hana/is_empty.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Xs, typename N>
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constexpr auto drop_front_exactly_t::operator()(Xs&& xs, N const& n) const {
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using It = typename hana::tag_of<Xs>::type;
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using DropFrontExactly = BOOST_HANA_DISPATCH_IF(drop_front_exactly_impl<It>,
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hana::Iterable<It>::value &&
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hana::IntegralConstant<N>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Iterable<It>::value,
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"hana::drop_front_exactly(xs, n) requires 'xs' to be an Iterable");
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static_assert(hana::IntegralConstant<N>::value,
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"hana::drop_front_exactly(xs, n) requires 'n' to be an IntegralConstant");
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#endif
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static_assert(N::value >= 0,
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"hana::drop_front_exactly(xs, n) requires 'n' to be non-negative");
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return DropFrontExactly::apply(static_cast<Xs&&>(xs), n);
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}
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template <typename Xs>
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constexpr auto drop_front_exactly_t::operator()(Xs&& xs) const {
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return (*this)(static_cast<Xs&&>(xs), hana::size_c<1>);
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}
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//! @endcond
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namespace detail {
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template <typename Xs, typename N>
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constexpr void check_dfe_overflow(Xs const& xs, N const&, hana::true_) {
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constexpr bool n_overflew_length = decltype(
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hana::is_empty(hana::drop_front(xs, hana::size_c<N::value - 1>))
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)::value;
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static_assert(!n_overflew_length,
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"hana::drop_front_exactly(xs, n) requires 'n' to be less than or "
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"equal to the number of elements in 'xs'");
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}
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template <typename Xs, typename N>
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constexpr void check_dfe_overflow(Xs const&, N const&, hana::false_) { }
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}
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template <typename It, bool condition>
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struct drop_front_exactly_impl<It, when<condition>> : default_ {
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template <typename Xs, typename N>
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static constexpr auto apply(Xs&& xs, N const& n) {
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auto result = hana::drop_front(static_cast<Xs&&>(xs), n);
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constexpr bool check_for_overflow =
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decltype(hana::is_empty(result))::value && N::value != 0;
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detail::check_dfe_overflow(xs, n, hana::bool_c<check_for_overflow>);
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return result; // NRVO applied
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_DROP_FRONT_EXACTLY_HPP
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