Inferring Nested Generic Parameter and Returning It from Function

Question

I have an IModelDefinition like this:

export interface IModelDefinition<MT extends Typegoose, QT> {
  model: new () => MT;
}

QT isn't directly used in the interface itself, but it is passed as a helper to other functions, like this so Typescript can infer the QT automatically:

public async getSingleMatch<MT extends Typegoose, QT>(
    definition: ModelDefinition<MT, QT>,
    doc: QT
): Promise<MT> ...

And I call the function like this:

// Account is a ModelDefinition<AccountClass, {identifier: string} and
// if I remove the identifier string, it gives an error as I expect it to.
const account = await getSingleMatch(Account, {
      identifier: params.identifier,
});

Everything is right until getting the result. The result is type of Typegoose , but it should be of type AccountClass instead. How can I solve this? Thanks for your help.

EDIT: To resolve misunderstanding; I can pass the types, but the whole reason I'm building this is to not to pass the types and make it infer automatically. Isn't there a way?

Answer 1

I think you should also pass the type while calling the function.

const account = await getSingleMatch<AccountClass, {identifier: string}>(Account, {identifier: params.identifier})

---

Now if you don't want the type to be passed every time you call the function and want it to infer the AccountClass , so just assign the default type AccountClass to the generic type.

public async getSingleMatch<MT extends Typegoose = AccountClass, QT>(
    definition: ModelDefinition<MT, QT>,
    doc: QT
): Promise<MT> ...