How to extend a TypeScript interface and unpartial it

Question

I want to be able to do the following:

interface Partials {
  readonly start?: number;
  readonly end?: number;
}

interface NotPartials extends Partials /*incorporate Unpartialing somehow */ {
  readonly somewhere: number;
}

Then, NotPartials would be:

readonly start: number;
readonly end: number;
readonly somewhere: number;

Notice how start and end are required now. Is this possible anyway?

Answer 1

Well, this is silly.

I think in TypeScript 2.8 this is possible:

interface Partials {
  readonly start?: number;
  readonly end?: number;
}

interface NotPartials extends Required<Partials> {
  readonly somewhere: number;
}