[cognisent]

TypeScript doesn't require a class to use it, though, because it's structurally typed. All that "implements Foo" in this example does is make sure that you get a type error on the definition of "One" if it doesn't have the members of "Foo".

If "Two" didn't have a "name: string" member, then the error would be on the call to "test".

    interface Foo {
        name: string
    }

    class One implements Foo {
        constructor(public name: string) {}
    }

    class Two {
        constructor(public name: string) {}
    }

    function test(thing: Foo): void {
        //...
    }

    test(new One('joe'));
    test(new Two('jane'));