Can the "spreadCall" function be effectively implemented? An enigma involving conditional typing and inference

One of the challenges I'm facing at work relates to a specific function. The function in question is the following:


    function spreadCall(f1, f2) {
        const args = f1();
        f2(...args);
    }

The issue is that we need f2 to accept an exact number of arguments (a tuple) in the same order as the output of f1. I've been struggling to find a solution for this problem. One approach I've thought of is to define different numbers of arguments like so:


    type Output<F> = 
         F extends ()=>[infer A0] ? (a0:A0)=>void :
         F extends ()=>[infer A0, infer A1] ? (a0:A0, a1:A1)=>void :
         F extends ()=>[infer A0, infer A1, infer A2] ? (a0:A0, a1:A1, a2:A2)=>void :
         never;
    // Add more argument definitions as needed ^^

    function spreadCall<InputF>(f1:InputF, f2:Output<InputF>) {
        // Your implementation here...
    }

The big question remains - is there a way to make it work with any number of arguments automatically?

Answer â„–1

If you're looking to achieve a specific functionality, one way to approach it is by utilizing a generic rest parameter type:

function spreadCall<A extends any[]>(f1: () => A, f2: (...args: A) => any) {
    const args = f1();
    f2(...args);
}

In this setup, the return value of f1 needs to adhere to a specific structure defined as a tuple, matching the parameter types expected by function f2:

declare function input(): [number, string]
declare function output(a: number, b: string): void;

spreadCall(input, output);

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