out_of_line_vtable.h

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#pragma once
 
#include "di/any/concepts/any_storable.h"
#include "di/any/concepts/interface.h"
#include "di/any/meta/method_erased_signature.h"
#include "di/any/vtable/erased_call.h"
#include "di/util/get.h"
#include "di/vocab/tuple/prelude.h"
 
namespace di::any {
struct OutOfLineVTable {
    template<typename Interface>
    class Invoke;
 
    template<typename... Methods>
    requires(concepts::Method<meta::Type<Methods>> && ...)
    class Invoke<meta::List<Methods...>> {
    private:
        using Storage = Tuple<meta::MethodErasedSignature<meta::Type<Methods>>*...>;
 
        template<typename Storage, typename T>
        constexpr static auto method_table =
            make_tuple(detail::ErasedCallImpl<meta::Type<Methods>, Storage, T>::call...);
 
    public:
        template<typename Storage, concepts::AnyStorable<Storage> T>
        constexpr static auto create_for() -> Invoke {
            return Invoke(util::addressof(method_table<Storage, T>));
        }
 
        constexpr Invoke() { reset(); }
 
        constexpr auto empty() const -> bool { return m_storage == nullptr; }
        constexpr void reset() { m_storage = nullptr; }
 
        template<concepts::OneOf<meta::Type<Methods>...> Method>
        constexpr auto operator[](Method) const {
            constexpr auto index = meta::Lookup<Method, meta::List<meta::Type<Methods>...>>;
            return util::get<index>(*m_storage);
        }
 
    private:
        constexpr Invoke(Storage const* storage) : m_storage(storage) {}
 
        Storage const* m_storage;
    };
};
}