Function Overloads

TypeScript's function overloads let you declare multiple call signatures for a single function, giving callers precise types per input:

function double(value: string):  string;
function double(value: number):  number;
function double(value: boolean): boolean;
// Implementation (not visible to callers):
function double(value: string | number | boolean): string | number | boolean {
  ...
}

const s = double('hi');   // TypeScript infers: string ✅
const n = double(5);      // TypeScript infers: number ✅
const b = double(true);   // TypeScript infers: boolean ✅

Without overloads, double would return string | number | boolean for every call — callers would always need to narrow.

Implement double

The TypeScript challenge: declare four overload signatures so each call site gets the exact return type.