function returns_nothing(): void { return; // valid } function returns_one(): void { return 1; // Fatal error: A void function must not return a value } function returns_null(): void { return null; // Fatal error: A void function must not return a value } https://wiki.php.net/rfc/void_return_type
of these types, such as integer, double and boolean add explicit scalar type support for parameter and return types add union types, such as int|false reserve other types such as numeric, mixed or scalar