A guide on how to identify the return type of a callback function in TypeScript

Looking at this function I've created

function computedLastOf<T>(cb: () => T[]) : Readonly<Ref<T | undefined>> {
  return computed(() => {
    const collection = cb();
    return collection[collection.length - 1];
  });
}

This function acts as a macro that produces a reactive value for a generic type T collection.

The issue here is the explicit <T> which requires the user to specify the type. It would be great if this could be inferred automatically. The output of this function will always be an element from the collection returned by the callback.

Is there a way to achieve automatic type inference like this?

Appreciate any guidance!

Answer №1

When utilizing a generic function, it is typically feasible to exclude the type parameter, leading to automatic inference. This can sometimes lead to errors, especially in more intricate scenarios where the system fails to detect certain nuances and infers a broader type than intended (though valid).

Consider using computedLastOf(arg) instead of explicitly specifying a type with

computedLastOf<someType>(arg)
.

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