Hello pmehro,
When the compiler faces the handle of class declaration which is not declared yet when the other class using that handle. It will reports Error.
Lets say class Y using the handle x , which is not declared yet, so it will report an Error.
To Rectify This solution Typedef is used.
Here is the Example for better interpretation.
class Y ;
X x; // refers to Class X, which is not yet defined
endclass
class X;
int i;
endclass
Below is the code to Resolve the Error.
typedef class X;
class Y ;
X x; // refers to Class X, which is not yet defined
endclass
class X;
int i;
endclass