zip_transform.h

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#pragma once
 
#include "di/container/view/empty.h"
#include "di/container/view/zip_transform_view.h"
#include "di/function/tag_invoke.h"
 
namespace di::container::view {
namespace detail {
    struct ZipTransformFunction;
 
    template<typename F, typename... Cons>
    concept CustomZipTransform = sizeof...(Cons) > 0 && concepts::TagInvocable<ZipTransformFunction, F, Cons...>;
 
    template<typename F, typename... Cons>
    concept EmptyZipTransform = sizeof...(Cons) == 0 && concepts::Invocable<meta::Decay<F>&> &&
                                concepts::Object<meta::Decay<meta::InvokeResult<meta::Decay<F>&>>>;
 
    template<typename F, typename... Cons>
    concept ViewZipTransform = sizeof...(Cons) > 0 && requires(F&& function, Cons&&... containers) {
        ZipTransformView(util::forward<F>(function), util::forward<Cons>(containers)...);
    };
 
    struct ZipTransformFunction {
        template<typename F, concepts::ViewableContainer... Cons>
        requires(CustomZipTransform<F, Cons...> || EmptyZipTransform<F, Cons...> || ViewZipTransform<F, Cons...>)
        constexpr auto operator()(F&& function, Cons&&... containers) const -> concepts::View auto {
            if constexpr (CustomZipTransform<F, Cons...>) {
                return function::tag_invoke(*this, util::forward<F>(function), util::forward<Cons>(containers)...);
            } else if constexpr (EmptyZipTransform<F, Cons...>) {
                return empty<meta::Decay<meta::InvokeResult<meta::Decay<F>&>>>();
            } else {
                return ZipTransformView { util::forward<F>(function), util::forward<Cons>(containers)... };
            }
        }
    };
}
 
constexpr inline auto zip_transform = detail::ZipTransformFunction {};
}
 
namespace di {
using view::zip_transform;
}