traits.h

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#pragma once

#include "../access_context.h"

namespace escad::detail
{

template<class T, class E>
class can_handle_event
{
    template<class U>
    static auto test(int) -> decltype(std::declval<U>().handle(std::declval<E>()), std::true_type{});

    template<class>
    static std::false_type test(...);

public:
    static constexpr auto value = std::is_same_v<std::true_type, decltype(test<T>(0))>;
};

template<class T, class E, class C>
class can_handle_event_with_context
{
    static C& get_context() noexcept;

    template<class U>
    static auto test(int) -> decltype(std::declval<U>().handle(std::declval<E>(), get_context()), std::true_type{});

    template<class>
    static std::false_type test(...);

public:
    static constexpr auto value = std::is_same_v<std::true_type, decltype(test<T>(0))>;
};

} // namespace fsm::detail