Understanding various generic types in Typescript

Imagine a scenario where I have a tool that provides types with the following structure:

type FunctionA<In, Out> = (input: In) => Out;

Additionally, there is another tool in the form of a method that has a mirrored format like this:

const funcB = <Out, In>(input: In) => input as any as Out;

What I aim to achieve is creating a function that can automatically infer types from the first tool and utilize them to call the second tool. While my attempt may not be accurate, the concept would look something like this:

const funcC = <Func extends FunctionA<infer I, infer O>>(input: I) => funcB<O, I>(input);

This would allow me to use it in the following way:

/** External Definition */
type A = FunctionA<string, number>;
/** External Definition */

funcC<A>('text');

Initially, I thought this would be straightforward, but I am struggling to find an effective approach.

Answer №1

Appreciate it, @jcalz, your guidance was spot on for what I needed to accomplish. The key lies in establishing helper conditional types for the proxy function:

type In<F extends FunctionA<any, any>> = F extends FunctionA<infer I, any> ? I : never;
type Out<F extends FunctionA<any, any>> = F extends FunctionA<any, infer O> ? O : never;

const funcC = <F extends FunctionA<any, any>>(input: In<F>) => funcB<Out<F>, In<F>>(input);

My apologies for the abstract explanation, this scenario has crossed my path multiple times in the past when trying to integrate different tools, but I hadn't found the opportunity to thoroughly address it. Unfortunately, I couldn't recall a specific example to include in the question without leaving out crucial details.

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