What strategies can be employed to improve generic inference skills?

Looking at the scenario provided below, how can we enhance code reusability in a manner similar to foobarA?

interface F<T, U extends string> { t: T, f: (u: U) => void }
declare const foo: <T, U extends string>(type: U) => F<T, U>;

// the following correctly types foobar, however 'bar' redundantly repeats.
const foobar = foo<string, 'bar'>('bar')

// ideally one would want the generic inference to be smarter and the
// following to work:
const foobarA = foo<string>('bar')

Answer №1

When it comes to TypeScript, there is a limitation in directly supporting partial type argument inference as discussed on microsoft/TypeScript#26242. If you have a generic function shaped like this:

declare const foo: <T, U extends string>(u: U) => F<T, U>;

You cannot call it in a way that manually specifies `T` while letting the compiler infer `U`, such as:

// const foobarA: F<string, unknown> ☹
const foobar = foo<string, "bar">("bar");

You are stuck with either specifying both type arguments redundantly or allowing the compiler to infer both arguments incorrectly.

...

In conclusion, both workarounds are viable options, but currying seems like the preferred approach unless finding an appropriate argument for the dummy parameter is simple for the caller.

Playground link to code

Answer №2

This code snippet will indeed compile without any errors. However, its effectiveness in achieving your desired outcome remains uncertain.

function createLogFunction<T extends string = string, S>(type: T) {
  return { 
    [type]: (arg: S) => console.log(arg)
  };
}

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