Method is

include/sol/lua_value.hpp:128–136

		template <typename T>
		bool is() const {
			int r = ref_value.registry_index();
			if (r == LUA_REFNIL)
				return meta::any_same<meta::unqualified_t<T>, lua_nil_t, nullopt_t, std::nullptr_t>::value ? true : false;
			if (r == LUA_NOREF)
				return false;
			auto pp = stack::push_pop(ref_value);
			return stack::check<T>(ref_value.lua_state(), -1, &no_panic);
		}
	};

	using array_value = typename lua_value::arr;