To what extent do typecheckers look into dynamically generated types/classes?

[samuelgoto]

(porting @Waldemar's comments into github issues)

@Waldemar: What about dynamically generated types?

@Waldemar: to what extent do typecheckers look into dynamically generated types/classes? For example:

class B {};
// TODO(goto): this actually doesn't work, come up with a better example.
eval("class A extends B {}");
var b: B = new A();
// Does this generate a type error in the typechecker?