Typescript interface overloading

What could be causing this error?

I am attempting to overload with typescript but despite reading the documentation, I am unable to pinpoint the error. Can someone offer some assistance?


export declare type TCallbackResponse<T> = ICallbackResponse<T>;

export type ICallbackResponse<T = string> = {
    (arg1: T, arg2: T, arg3: T): Promise<void>;
    (arg1: T, arg2: T): Promise<void>;
}


function handle<T = string>(name: string, call: ICallbackResponse<T>): void {

}

async function message(pattern: string, channel: string, message: string): Promise<void>
async function message(channel: string, message: string): Promise<void> {

}

async function pmessage(pattern: string, channel: string, message: string): Promise<void> {

}

handle('message', message) // Argument of type '(pattern: string, channel: string, message: string) => Promise<void>' is not assignable to parameter of type 'ICallbackResponse<string>'.(2345)
handle('message', pmessage) // Argument of type '(pattern: string, channel: string, message: string) => Promise<void>' is not assignable to parameter of type 'ICallbackResponse<string>'.(2345)

Check out the code here: here

Answer №1

According to information from the official documentation, the methods described in your case are referred to as the Implementation Signatures rather than Overload signatures -

async function message(channel: string, message: string): Promise<void> {
    
}

async function pmessage(pattern: string, channel: string, message: string): Promise<void> {

}

As outlined in the Documentation -

The signature of the implementation is not visible from the outside. When writing an overloaded function, you should always have two or more signatures above the implementation of the functions.

In your situation, since there are multiple call signatures and not all calls match all the signatures in ICallbackResponse, it's important to note that none of the signatures match with

(arg1: T, arg2: T): Promise<void>;
due to the missing third parameter.

Furthermore, upon closer inspection, it seems unnecessary to include the

(arg1: T, arg2: T): Promise<void>;
type in the ICallbackResponse in your specific case.

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