gistfile1.ts

// inspired: http://journal.stuffwithstuff.com/2013/04/23/playing-with-generics-in-typescript-0.9.0/

class Base {
	foo() : void {}
}
// If `Derived' has no addional method, we'll get different results
class Derived extends Base {
	bar() : void {}
}

var a : Base = new Derived();
var b : Derived = new Base(); // error

class Box<T> {
  constructor(public value:T) {}
};

// Covariance
var c : Box<Base> = new Box<Derived>(null);
var d : Box<Derived> = new Box<Base>(null); // error
var e : () => Base = () => { return new Derived };
var f : () => Derived = () => { return new Base }; // error

// Function argument bivariance
var g : (x:Base) => void = (x:Derived) => { x.bar() }; // no error, but `g(new Base)' causes a runtime error!
var h : (x:Derived) => void = (x:Base) => {};

// Extra parameter subtyping
var i : (x:Base, y:number) => void = (arg:Base) => {};
var j : (x:Base) => void = (arg:Base, additional:number) => {}; // error