// @target: es2015
// no errors expected

class C<T extends Date> {
    constructor(public data: T) { }
    foo<U extends T>(x: U) {
        return x;
    }
}

interface Foo extends Date {
    foo: string;
}

var y: Foo = {} as Foo;
var c = new C(y);
var r = c.foo(y);