Result of a generic function

Question

Result of a generic function

I've been working on adjusting the getResults function to return the correct type, but I'm currently faced with this issue:

interface IResponse<T> {
    result: T;
}

type FnType<P, R> = (params: P) => R;

const r1: IResponse<string[]> = { result: ['123'] };
const r2: IResponse<number[]> = { result: [456] };

const getResults = <T, R extends IResponse<T[]>, P>(fn: FnType<P, R>, params: P): T[] => {
    return [
        ...fn(params).result,
        ...fn(params).result
    ];
};

const getValue = <T>(r: IResponse<T>) => r;

// The returned type is unknown[]
// How can we modify it to return string[]?
getResults(getValue, r1);

// The returned type is unknown[]
// How can we modify it to return number[]?
getResults(getValue, r2);

Playground

This code is simply a demonstration; in a real-world scenario, the getResults function is utilized for merging results from paginated requests (where fn acts as a request function).

typescript generics

Answer 1

Answer №1

It's uncertain if this code snippet covers all the necessary aspects for production use. However, the return type seems adequate in its current form:

interface IResponse<T> {
    result: T;
}

type FnType<P, R> = (params: P) => R;

const r1: IResponse<string[]> = { result: ['123'] };
const r2: IResponse<number[]> = { result: [456] };

const myResults = <P,R>(fn: FnType<P,IResponse<R[]>>, params: P): R[] => {
     return [
        ...fn(params).result,
        ...fn(params).result
    ];
}

const getValue = <T>(r: IResponse<T>) => r;

myResults(getValue, r1);

myResults(getValue, r2);

Playground link

Edit: The reason behind the inaccurate IntelliSense behavior of the provided code is not clear to me.

However, it appears that three generic types T, R, and P were used. My interpretation suggests that only two types are essential, representing the parameters and the method's result.

In essence, whatever type is contained within the getValue's IResponse will serve as the final output of the myResults function.

Answer 2

It's uncertain if this code snippet covers all the necessary aspects for production use. However, the return type seems adequate in its current form:

interface IResponse<T> {
    result: T;
}

type FnType<P, R> = (params: P) => R;

const r1: IResponse<string[]> = { result: ['123'] };
const r2: IResponse<number[]> = { result: [456] };

const myResults = <P,R>(fn: FnType<P,IResponse<R[]>>, params: P): R[] => {
     return [
        ...fn(params).result,
        ...fn(params).result
    ];
}

const getValue = <T>(r: IResponse<T>) => r;

myResults(getValue, r1);

myResults(getValue, r2);

Playground link

Edit: The reason behind the inaccurate IntelliSense behavior of the provided code is not clear to me.

However, it appears that three generic types T, R, and P were used. My interpretation suggests that only two types are essential, representing the parameters and the method's result.

In essence, whatever type is contained within the getValue's IResponse will serve as the final output of the myResults function.

Result of a generic function

Answer №1

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