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Diffstat (limited to 'boost/hana/drop_front_exactly.hpp')
-rw-r--r-- | boost/hana/drop_front_exactly.hpp | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/boost/hana/drop_front_exactly.hpp b/boost/hana/drop_front_exactly.hpp new file mode 100644 index 0000000000..61b43c4e2a --- /dev/null +++ b/boost/hana/drop_front_exactly.hpp @@ -0,0 +1,85 @@ +/*! +@file +Defines `boost::hana::drop_front_exactly`. + +@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_DROP_FRONT_EXACTLY_HPP +#define BOOST_HANA_DROP_FRONT_EXACTLY_HPP + +#include <boost/hana/fwd/drop_front_exactly.hpp> + +#include <boost/hana/bool.hpp> +#include <boost/hana/concept/integral_constant.hpp> +#include <boost/hana/concept/iterable.hpp> +#include <boost/hana/config.hpp> +#include <boost/hana/core/dispatch.hpp> +#include <boost/hana/drop_front.hpp> +#include <boost/hana/integral_constant.hpp> +#include <boost/hana/is_empty.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! @cond + template <typename Xs, typename N> + constexpr auto drop_front_exactly_t::operator()(Xs&& xs, N const& n) const { + using It = typename hana::tag_of<Xs>::type; + using DropFrontExactly = BOOST_HANA_DISPATCH_IF(drop_front_exactly_impl<It>, + hana::Iterable<It>::value && + hana::IntegralConstant<N>::value + ); + + #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS + static_assert(hana::Iterable<It>::value, + "hana::drop_front_exactly(xs, n) requires 'xs' to be an Iterable"); + + static_assert(hana::IntegralConstant<N>::value, + "hana::drop_front_exactly(xs, n) requires 'n' to be an IntegralConstant"); + #endif + + static_assert(N::value >= 0, + "hana::drop_front_exactly(xs, n) requires 'n' to be non-negative"); + + return DropFrontExactly::apply(static_cast<Xs&&>(xs), n); + } + + template <typename Xs> + constexpr auto drop_front_exactly_t::operator()(Xs&& xs) const { + return (*this)(static_cast<Xs&&>(xs), hana::size_c<1>); + } + //! @endcond + + namespace detail { + template <typename Xs, typename N> + constexpr void check_dfe_overflow(Xs const& xs, N const&, hana::true_) { + constexpr bool n_overflew_length = decltype( + hana::is_empty(hana::drop_front(xs, hana::size_c<N::value - 1>)) + )::value; + static_assert(!n_overflew_length, + "hana::drop_front_exactly(xs, n) requires 'n' to be less than or " + "equal to the number of elements in 'xs'"); + } + + template <typename Xs, typename N> + constexpr void check_dfe_overflow(Xs const&, N const&, hana::false_) { } + } + + template <typename It, bool condition> + struct drop_front_exactly_impl<It, when<condition>> : default_ { + template <typename Xs, typename N> + static constexpr auto apply(Xs&& xs, N const& n) { + auto result = hana::drop_front(static_cast<Xs&&>(xs), n); + constexpr bool check_for_overflow = + decltype(hana::is_empty(result))::value && N::value != 0; + + detail::check_dfe_overflow(xs, n, hana::bool_c<check_for_overflow>); + + return result; // NRVO applied + } + }; +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_DROP_FRONT_EXACTLY_HPP |