Cannot use valid union type as a map's key

TypeScript Version: 3.0

Search Terms:

map
union type
string | number

Code

const m: { [key: string | number]: any };

class C<K extends string | number> {
    private _m: { [key: K]: any };
}

Expected behavior:

It compiles.

Actual behavior:

An index signature parameter type must be 'string' or 'number'.
(parameter) key: string | number

Playground Link: http://www.typescriptlang.org/play/#src=const%20m%3A%20%7B%20%5Bkey%3A%20string%20%7C%20number%5D%3A%20any%20%7D%3B%0D%0A%0D%0Aclass%20C%3CK%20extends%20string%20%7C%20number%3E%20%7B%0D%0A%20%20%20%20private%20_m%3A%20%7B%20%5Bkey%3A%20K%5D%3A%20any%20%7D%3B%0D%0A%7D

Probably fixed by #26797

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

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