drop.h

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#pragma once
 
#include "di/container/algorithm/min.h"
#include "di/container/interface/reconstruct.h"
#include "di/container/interface/ssize.h"
#include "di/container/view/drop_view.h"
#include "di/function/curry_back.h"
#include "di/function/tag_invoke.h"
 
namespace di::container::view {
namespace detail {
    struct DropFunction {
        template<concepts::ViewableContainer Con, concepts::ConvertibleTo<meta::ContainerSSizeType<Con>> Diff>
        constexpr auto operator()(Con&& container, Diff&& difference) const -> concepts::View auto {
            if constexpr (concepts::TagInvocable<DropFunction, Con, Diff>) {
                return function::tag_invoke(*this, util::forward<Con>(container), util::forward<Diff>(difference));
            } else if constexpr (concepts::SizedContainer<Con> && concepts::RandomAccessContainer<Con> &&
                                 concepts::BorrowedContainer<Con> &&
                                 concepts::ContainerIteratorReconstructibleContainer<Con, meta::RemoveCVRef<Con>,
                                                                                     meta::ContainerIterator<Con>,
                                                                                     meta::ContainerIterator<Con>>) {
                return container::reconstruct(
                    in_place_type<meta::RemoveCVRef<Con>>, util::forward<Con>(container),
                    container::begin(container) +
                        container::min(container::ssize(container),
                                       static_cast<meta::ContainerSSizeType<Con>>(difference)),
                    container::end(container));
            } else {
                return DropView { util::forward<Con>(container),
                                  static_cast<meta::ContainerSSizeType<Con>>(difference) };
            }
        }
    };
}
 
constexpr inline auto drop = function::curry_back(detail::DropFunction {}, meta::c_<2ZU>);
}
 
namespace di {
using view::drop;
}