TypeScript: Can I infer number index value type?-CodePudding

I created a helper function to convert an object of numbered keys to a Map:

interface IndexedObject {
    [index: number]: unknown;
};

const objectToIndexedMap = (indexedObject: IndexedObject) => new Map(
    Object.entries(indexedObject).map(
        ([ index, field ]) => [ Number(index), field ]
    )
);

I use it to convert objects I'm getting from the API to a more convenient Map, where I don't need to deal with string keys anymore. The problem is that the returned type is Map<number, any>, while I'd like to use the type of those values in IndexedObject.

Is it possible to get that type and make my function return this specific type for Map values?

So for example this would throw an error:

interface IndexedNumbers {
    [index: number]: number;
}

const indexedNumbers: IndexedNumbers = api.numbers; // pseudocode
const map = objectToIndexedMap(indexedNumbers);
const foo = map.get(0)!.toUpperCase(); // This should throw an error

Of course I know I can hard-type it:

const map: Map<number, number> = objectToIndexedMap(indexedNumbers);

But I'd love TypeScript to do that for me. Is it possible?

CodePudding user response：

I think It can be achieved with the help of templates.

like this:

interface IndexedObject<T> {
    [index: number]: T;
};

const objectToIndexedMap = <T>(indexedObject: IndexedObject<T>) => new Map<number, T>(
    Object.entries(indexedObject).map(
        ([ index, field ]) => [ Number(index), field ]
    )
);

Usage:

interface IndexedNumbers {
    [index: number]: number;
}

const indexedNumbers: IndexedNumbers = api.numbers; // pseudocode
const map = objectToIndexedMap(indexedNumbers);
const foo = map.get(0)!.toUpperCase(); // This should throw an error

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