intrusive_ptr_cpo.h

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#pragma once
 
#include "di/function/tag_invoke.h"
#include "di/types/prelude.h"
 
namespace di::vocab {
namespace detail {
    struct IntrusivePtrIncrement {
        template<typename Tag, typename T>
        requires(concepts::TagInvocable<IntrusivePtrIncrement, InPlaceType<Tag>, T*>)
        constexpr void operator()(InPlaceType<Tag>, T* ptr) const {
            return function::tag_invoke(*this, in_place_type<Tag>, ptr);
        }
    };
 
    struct IntrusivePtrDecrement {
        template<typename Tag, typename T>
        requires(concepts::TagInvocable<IntrusivePtrDecrement, InPlaceType<Tag>, T*>)
        constexpr void operator()(InPlaceType<Tag>, T* ptr) const {
            return function::tag_invoke(*this, in_place_type<Tag>, ptr);
        }
    };
}
 
constexpr inline auto intrusive_ptr_increment = detail::IntrusivePtrIncrement {};
constexpr inline auto intrusive_ptr_decrement = detail::IntrusivePtrDecrement {};
 
namespace detail {
    template<typename T, typename Tag>
    concept IntrusivePtrValid = requires(T* pointer) {
        intrusive_ptr_increment(in_place_type<Tag>, pointer);
        intrusive_ptr_decrement(in_place_type<Tag>, pointer);
    };
}
}