Add support for generic types on a index accessor about typescript HOT 4 CLOSED

@RyanCavanaugh Logically the method you suggested should behave exactly the same as the one I mentioned above. However when I tested with the code below, only the key and value part works correctly, the overlay does not. Invoking a function on the overlay produces an error message:

This expression is not callable. Type 'String' has no call signatures.

The code I used:

type SuperRecord<Key extends keyof any, Value, Overlay = {}> = {
	[E in Key]: E extends keyof Overlay ? Overlay[E]: Value;
};
interface K extends SuperRecord<string, string, { func1(): void; }> {
}
let k: K = ...
k["str"] = "val"; // works fine
k.func1(); // error
k.toString(); // works fine

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This seems like just an exact duplicate of #17867.

You can already write

type SuperRecord<Key extends keyof any, Value, Overlay = {}> = {
    [E in Key]: E extends keyof Overlay ? Overlay[E]: Value;
};

to get the generic behavior on an index signature's output type, nothing new is needed.

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Right, you'd still need rest signatures. But K would be declared as this:

type O = { func1(): void; };
interface K extends SuperRecord<keyof O, string, O> {
  // TODO: Be able to uncomment.
  // [...rest: string]: string
}

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

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