I admit this is a bit of a syntactic nit, but in the  $object_reference->method and  ClassName->method OO cases, doesn't the  -> operator as unambiguously indicate function invocation (both to compiler and to programmer) as the parentheses in the  func() case? I.e., always writing  $obj->method without any parentheses is the same as always writing  func() with its empty parentheses. (Although I certainly agree that  $obj->method() is perfectly valid.)