covariant subtype values with @template

A couple of useful tricks using @template.

Return the calling subtype from a super class method:

/** @constructor */ function Foo() {}

/**

• @this {THIS}
• @return {THIS}
• @template THIS */ Foo.prototype.method = function() { return this; }

/** @constructor @extends {Foo} */ function Bar() {} Bar.prototype = new Foo();

var x = new Bar().method(); // x is of type "Bar"