begin.h

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#pragma once
 
#include "di/container/concepts/iterator.h"
#include "di/container/interface/enable_borrowed_container.h"
#include "di/function/pipeable.h"
#include "di/function/tag_invoke.h"
#include "di/meta/core.h"
#include "di/meta/language.h"
#include "di/meta/util.h"
#include "di/util/forward.h"
 
namespace di::container {
struct BeginFunction;
 
namespace detail {
    template<typename T>
    concept ArrayBegin = concepts::LanguageArray<meta::RemoveReference<T>>;
 
    template<typename T>
    concept CustomBegin = concepts::TagInvocable<BeginFunction, T> &&
                          concepts::Iterator<meta::Decay<meta::TagInvokeResult<BeginFunction, T>>>;
 
    template<typename T>
    concept MemberBegin = requires(T&& container) {
        { util::forward<T>(container).begin() } -> concepts::Iterator;
    };
    concept MemberBegin = requires(T&& container) {…}
}
 
struct BeginFunction : function::pipeline::EnablePipeline {
    template<typename T>
    requires(enable_borrowed_container(types::in_place_type<meta::RemoveCV<T>>) &&
             (detail::ArrayBegin<T> || detail::CustomBegin<T> || detail::MemberBegin<T>) )
    constexpr auto operator()(T&& container) const {
        if constexpr (detail::ArrayBegin<T>) {
            return container + 0;
        } else if constexpr (detail::CustomBegin<T>) {
            return function::tag_invoke(*this, util::forward<T>(container));
        } else {
            return util::forward<T>(container).begin();
        }
    }
    constexpr auto operator()(T&& container) const  {…}
};
struct BeginFunction : function::pipeline::EnablePipeline {…};
 
constexpr inline auto begin = BeginFunction {};
}
 
namespace di {
using container::begin;
}