Type false is not assignable to type this[keyof this] (in 2.1.4)

[newapx]

TypeScript Version: 2.1.4

Code

// A *self-contained* demonstration of the problem follows...
export class ClassA {
  public clean() {
    for (let prop in this) {
      if (typeof this[prop] === "boolean")  this[prop] = false;
    }
  }
}

Expected behavior:
Compiled without error

Actual behavior:
Error Type false is not assignable to type this[keyof this]

[dead-claudia]

Try adding interface BoolMap { [key: string]: boolean; } and change the initial class declaration to class ClassA implements BoolMap. TypeScript doesn't know that ClassA, or subclasses thereof, could even have any dynamic boolean properties, because it can only infer so much. Alternatively, you could use a temporary reference and cast the stored value to {[key: string]: boolean} & this.

(Oh, and you're iterating the prototype chain with that; might be a good idea to guard that with hasOwnProperty.)

[RyanCavanaugh]

Should be narrowing this[prop] in the body of the if

[mhegazy]

this is a duplicate of #10530. element access expressions are not narrowed.

[newapx]

Thank you for the recommendation, but I'm such solutions are not suitable.
I used (<any>this)[prop] = false;