Implementation of a function in Typescript that can be defined with a

I am currently diving into the Typescript specification and I'm facing a challenge in creating a functional implementation for describable functions.

https://www.typescriptlang.org/docs/handbook/2/functions.html

The provided example lacks completeness as it does not demonstrate the necessary code for executing and implementing the function signature. In the doSomething function, fn() is executed but the example fails to illustrate how it's called or what values are passed in. How would a call to doSomething be structured? And what would the signature of an instance of DescribableFunction look like?

type DescribableFunction = {
  description: string;
  (someArg: number): boolean;
};

function doSomething(fn: DescribableFunction) {
  console.log(fn.description + " returned " + fn(6));
}
// To Be Determined: Invoke doSomething and provide an instance of DescribableFunction with an implementation of the signature (someArg: number): boolean.

Answer №1

To solve this problem, you just need to provide a function that aligns with the type declaration

function IsNegative (someArg: number) : boolean {return someArg<0 };
IsNegative.description = "returns true if the input is negative";
doSomething(IsNegative)

Expected Outcome

The function should return true if the input is negative, but it returned false instead

Access Playground link here

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