TypeScript - passing a specific type of a union type to a nested function

const function = <T>(
  input: string | ArrayLike<T>
) => (output: string | ArrayLike<T>, position = 0) => {
  // perform operations with input and output
}

const result = function ('abc')

In this scenario, the resulting value is assigned as :

(output: string | ArrayLike<string>, position? number) => void
However, I am seeking for the outcome to be defined as
(output: string, position? number) => void
, adhering to the type of input supplied to function which was a string.

Additionally, I comprehend why the generic type T is perceived as a string - but my requirement demands an ArrayLike of T or a string exclusively and not a combination of both...

This specification is necessary to streamline the return type of a call to result.

Your assistance on this matter would be greatly appreciated ;)

Answer №1

If you want to make use of an overloaded function, here is one possible approach:

function myFunction(input: string): (output: string) => void;
function myFunction<T>(input: ArrayLike<T>): (output: ArrayLike<T>) => void;
function myFunction<T>(input: string | ArrayLike<T>) { 
  return (output: string | ArrayLike<T>, index = 0) => {
    // perform operations with input and output
  };
}

const result = myFunction('abc')  // (output: string) => void

This method will provide the correct types for calls to myFunction, although handling union types within the implementation of myFunction is still required.

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