Type Inference in for... in combined with typeof

<!-- BUGS: Please use this template. --> **TypeScript Version:** 2.1.4 The following code gives an error in TS 2.1: It's not really nice code, but I think it should work never the less :) ```TypeScript for (var a in this) { if (typeof this[a] === "function" && !ko.isObservable(this[a])) this[a] = this[a].bind(this); } ``` **Expected behavior:** I would expect this[a] to be typed as this[keyof this] & Function: ```TypeScript for (var a in this) { if (typeof this[a] === "function" && !ko.isObservable(this[a])) this[a] =( <this[keyof this] & Function> this[a]).bind(this); } ``` **Actual behavior:** It gives an error, as of TS 2.1, it worked in TS 2.0 (because mapped types did not exist, this[a] was typed as any)