Why are instance variables defined in the header file in Objective-C

Question

I can understand defining the functions in the @interface of the header file, but why the instance variables? Shouldn\'t the instance variables be private, only accessible

Answer 1

I think it is a technical issue. If I understand correctly, a Objective-C class is just a fancy C struct. And for a struct to be used its size must be known. (Like how would sizeof() work otherwise)