genericSpecializations3.ts(9,5): error TS2416: Property 'foo' in type 'IntFooBad' is not assignable to the same property in base type 'IFoo<number>'.
  Type '(x: string) => string' is not assignable to type '(x: number) => number'.
    Types of parameters 'x' and 'x' are incompatible.
      Type 'number' is not assignable to type 'string'.
genericSpecializations3.ts(9,30): error TS2322: Type 'null' is not assignable to type 'string'.
genericSpecializations3.ts(15,30): error TS2322: Type 'null' is not assignable to type 'number'.
genericSpecializations3.ts(21,30): error TS2322: Type 'null' is not assignable to type 'string'.
genericSpecializations3.ts(28,1): error TS2322: Type 'StringFoo2' is not assignable to type 'IntFoo'.
  Types of property 'foo' are incompatible.
    Type '(x: string) => string' is not assignable to type '(x: number) => number'.
      Types of parameters 'x' and 'x' are incompatible.
        Type 'number' is not assignable to type 'string'.
genericSpecializations3.ts(29,1): error TS2322: Type 'IntFoo' is not assignable to type 'StringFoo2'.
  Types of property 'foo' are incompatible.
    Type '(x: number) => number' is not assignable to type '(x: string) => string'.
      Types of parameters 'x' and 'x' are incompatible.
        Type 'string' is not assignable to type 'number'.
genericSpecializations3.ts(33,23): error TS2322: Type 'null' is not assignable to type 'T'.
  'T' could be instantiated with an arbitrary type which could be unrelated to 'null'.


==== genericSpecializations3.ts (7 errors) ====
    interface IFoo<T> {
        foo(x: T): T;
    }
    
    declare var iFoo: IFoo<number>;
    iFoo.foo(1);
    
    class IntFooBad implements IFoo<number> { // error
        foo(x: string): string { return null; }
        ~~~
!!! error TS2416: Property 'foo' in type 'IntFooBad' is not assignable to the same property in base type 'IFoo<number>'.
!!! error TS2416:   Type '(x: string) => string' is not assignable to type '(x: number) => number'.
!!! error TS2416:     Types of parameters 'x' and 'x' are incompatible.
!!! error TS2416:       Type 'number' is not assignable to type 'string'.
                                 ~~~~~~
!!! error TS2322: Type 'null' is not assignable to type 'string'.
    }
    
    declare var intFooBad: IntFooBad;
    
    class IntFoo implements IFoo<number> {
        foo(x: number): number { return null; }
                                 ~~~~~~
!!! error TS2322: Type 'null' is not assignable to type 'number'.
    }
    
    declare var intFoo: IntFoo;
    
    class StringFoo2 implements IFoo<string> {
        foo(x: string): string { return null; }
                                 ~~~~~~
!!! error TS2322: Type 'null' is not assignable to type 'string'.
    }
    
    declare var stringFoo2: StringFoo2;
    stringFoo2.foo("hm");
    
    
    intFoo = stringFoo2; // error
    ~~~~~~
!!! error TS2322: Type 'StringFoo2' is not assignable to type 'IntFoo'.
!!! error TS2322:   Types of property 'foo' are incompatible.
!!! error TS2322:     Type '(x: string) => string' is not assignable to type '(x: number) => number'.
!!! error TS2322:       Types of parameters 'x' and 'x' are incompatible.
!!! error TS2322:         Type 'number' is not assignable to type 'string'.
    stringFoo2 = intFoo; // error
    ~~~~~~~~~~
!!! error TS2322: Type 'IntFoo' is not assignable to type 'StringFoo2'.
!!! error TS2322:   Types of property 'foo' are incompatible.
!!! error TS2322:     Type '(x: number) => number' is not assignable to type '(x: string) => string'.
!!! error TS2322:       Types of parameters 'x' and 'x' are incompatible.
!!! error TS2322:         Type 'string' is not assignable to type 'number'.
    
    
    class StringFoo3 implements IFoo<string> { // error
        foo<T>(x: T): T { return null; }
                          ~~~~~~
!!! error TS2322: Type 'null' is not assignable to type 'T'.
!!! error TS2322:   'T' could be instantiated with an arbitrary type which could be unrelated to 'null'.
    }
    var stringFoo3: StringFoo3;