extendedInterfaceGenericType.ts(9,20): error TS2454: Variable 'alpha' is used before being assigned.


==== extendedInterfaceGenericType.ts (1 errors) ====
    interface Alpha<T> {
        takesArgOfT(arg: T): Alpha<T>;
        makeBetaOfNumber(): Beta<number>;
    }
    interface Beta<T> extends Alpha<T> {
    }
    
    var alpha: Alpha<number>;
    var betaOfNumber = alpha.makeBetaOfNumber();
                       ~~~~~
!!! error TS2454: Variable 'alpha' is used before being assigned.
    betaOfNumber.takesArgOfT(5);
    