copyable_function() noexcept = default;

copyable_function(copyable_function const& other);

copyable_function(copyable_function&& other) noexcept;

copyable_function(std::nullptr_t value) noexcept;

template<class Func>
copyable_function(Func&& f)
requires (!std::is_same_v<std::remove_cvref_t<Func>, copyable_function> &&
                 !_is_in_place_type<std::remove_cvref_t<Func>>::value && is_callable_from<std::decay_t<Func>>);

template<
    class T,
    class... _Args>
explicit
copyable_function(
    std::in_place_type_t<T>,
    _Args...&&... args)
requires (is_callable_from<std::decay_t<T>>);

template<
    class T,
    class U,
    class... _Args>
explicit
copyable_function(
    std::in_place_type_t<T>,
    std::initializer_list<U> il,
    _Args...&&... args)
requires (is_callable_from<std::decay_t<T>>);