Type inference for method overrides in derived classes

[dru89]

TypeScript Version: 2.4.0

Code

interface IPage {
    method: (ev: string | number) => any;
}

class Page implements IPage {
    method(e): any {
        // this "e" is implicitly any
    }
}

let x = new Page();
x.method = (e) => {
    // this "e" is inferred to be 'string | number'
}

Expected behavior:
The method override in Page should be inferred type string | number.

Actual behavior:
The method override in Page is implicitly the any type.

This seems like it should instead infer the parent type, because

1. instance overrides already have this sort of inference (see the Contextual Type example about window.onmousedown), and
2. if the class's override signature was something like method(e: object): any, there would be an error that says the class wasn't matching the interface's signature. (Class 'Page' incorrectly implements interface 'IPage'.)

[dru89]

My apologies if this either isn't a bug (or feature request) or it's already been closed in a separate ticket.

I wasn't able to really find anything related to this in search, and it seemed sort of like a bug to me.

[DanielRosenwasser]

It's not easy to find - check out #1373. Unfortunately we weren't able to solve this, but I think we're still considering some ideas here.

[dru89]

Thanks for pointing that ticket out (and the rabbit hole of tickets that I found that came from it).

Should I subscribe to #10610 as a potential solution and to #10570 as the open ticket for this dupe? I can definitely see why this is hard to solve. 😄

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.