Allow forwarding arguments to constructor for unexpected creation

Author: StormBytePP

lib/public/StormByte/expected.hxx

@@ -106,4 +106,27 @@ namespace StormByte {
 			std::make_shared<E>(std::move(formatted_message))
 		);
 	}
+
+	/**
+	 * @brief Construct an `std::unexpected` by forwarding constructor args into `E`.
+	 *
+	 * This overload allows calls like `Unexpected<MyError>(arg1, arg2)` and will
+	 * construct a `MyError` in-place using the forwarded arguments and store it
+	 * inside a `std::shared_ptr` returned inside `std::unexpected`.
+	 *
+	 * The overload is SFINAE-constrained to avoid ambiguity with the existing
+	 * `Unexpected(E&&)` overload when a single argument would directly match
+	 * that overload.
+	 */
+
+	template <typename E, typename... Args>
+	auto Unexpected(Args&&... args)
+	-> std::enable_if_t<
+		!(sizeof...(Args) == 1 && std::is_constructible_v<std::decay_t<E>, Args&&...>),
+		std::unexpected<std::shared_ptr<std::decay_t<E>>>
+	> {
+		return std::unexpected<std::shared_ptr<std::decay_t<E>>>(
+			std::make_shared<std::decay_t<E>>(new std::decay_t<E>(std::forward<Args>(args)...)) 
+		);
+	}
 }