打字稿泛型，未知的嵌套函数参数

Question

i have som problem with generic function which has function with unknown param as param.

export const inject = <I,V>(fn:<U>(input?:U) => V, resolveWithPayload: boolean, resolveArgs?: I) => <R>(payload:R):R => {
    resolveWithPayload ? fn(payload) : resolveArgs ? fn(resolveArgs) : fn();
    return  payload;
};

const fn = (value:number):number => {
    propertyToMutate = value;
    return propertyToMutate;
}

const res =_fish.inject(fn,false,60)(50);
but calling it ends with :

Argument of type '(value: number) => number' is not assignable to parameter of type '(input?: U) => number'. Types of parameters 'value' and 'input' are incompatible. Type 'U' is not assignable to type 'number'.

if i change code this way:

export const inject = <I,V,U>(fn:(input?:U) => V, resolveWithPayload: boolean, resolveArgs?: I) => <R>(payload:R):R => {
    resolveWithPayload ? fn(payload) : resolveArgs ? fn(resolveArgs) : fn();
    return  payload;
};

it ends by type definition error in inject itself like:

TS2345: Argument of type 'R' is not assignable to parameter of type 'U'.

TS2345: Argument of type 'I' is not assignable to parameter of type 'U'.

So what can i do, if i dont know type of input of "fn" ?

thanks

Answer 1

The first error is caused because inject expects a function with signature <U>(input?: U) => V , but the one you provided has signature (value: number) => number . In other words, inject expects that fn is a generic function over the type U that accepts a parameter of type U | undefined U | undefined , but the fn that you pass to it accepts a parameter of type number .

It's hard to know what exactly you're trying to accomplish with all of these generics, but perhaps you're looking for something like this:

export const inject = <U>(fn:(input?:U) => U, resolveWithPayload: boolean, resolveArgs?: U) => (payload:U):U => {
    resolveWithPayload ? fn(payload) : resolveArgs ? fn(resolveArgs) : fn();
    return payload;
};

const fn = (value:number = 0):number => {
    propertyToMutate = value;
    return propertyToMutate;
}

Notice that number is the only required type parameter