How to get type from the return of a function?-CodePudding

I'm trying to make a pseudo pipeline in typscript. The idea is that I would have a function that returns me an object. Then I would pass this object to other functions that can process this object.

The function signature would be something like this:

type FirstFunc<T> = () => T;
type Pipeline<T> = ((obj: T) => T)[]

const objPipeLine<T> = (firstFunc: FirstFunc<T>, pipeline: Pipeline<T>): T

But I don't want to provide the generic to this function. I want it to know what type of object the first function would return and use it as my T generic. Something like an implicit typing, the functions in the Pipeline should only accept parameters matching the kind of object my first function returns.

CodePudding user response：

FIrst of all this syntax is wrong: const objPipeLine<T>.

If you want to infer function argument, you should do const objPipeLine=<T>()=>{}.

Just put generic right after equal sign.

COnsider this example:

type FirstFunc<T> = () => T;
type Pipeline<T> = ((obj: T) => T)[]

const objPipeLine = <Return,>(firstFunc: FirstFunc<Return>, pipeline: Pipeline<Return>) => {}

const result = objPipeLine(
    () => ({ age: 42 }),
    [(obj) => obj]
)

Playground

I have created Return generic and let TS to infer it. If you hover your mouse on obj in [(obj) => obj] you will see that it is infered as {age: number}.

If you are interested in typing pipeline function you can check my article, this answer and this answer

CodePudding user response：

That's what typescript is made for, to specify them types, to assign a type to the return type we use ReturnType

type some=ReturnType<FirstFunc<T>>