interface I {
    fn: <T>(t: T) => void;
}
interface X {
    x: number;
}
function toI<T extends X>() : I {
    return {
        fn: (t: T) => { // <-- expected a warning from the compiler that the type constraint cannot be enforced
            alert(t.x);
        }
    };
}
function test(i: I): void {
    i.fn({}); // <-- problem unnoticed
}
test(toI<X>()); // displays "undefined"