I have a map that contains different types (string, objects, …) of values, under different types (string, Class, …) of key.

When the key is a class, the value is always an instance of that class.

I’ve tried to write a function that correctly type its return value when known, but it doesn’t work when the class constructor takes parameters:

const map = new Map();

function test<T>(key: new (...args: any[]) => T): T;
function test<T>(key: unknown): T
function test(key: unknown) {
  return map.get(key);
}

// test begin here

class A {}
class B {
  constructor(public foo: string) {}
}

const aaa = test(A) //< Correctly typed as `A`
const bbb = test(B) //< Incorrectly typed as `unknown`
const ccc = test('C') //< Correctly typed as `unknown`
const ddd = test<string>('D') //< Correctly typed as `string`

So the class B doesn’t seem to be recognized by the first function overloading, but what I cannot understand is that if I remove the second function overload, then b is correctly typed as B (but then calling the function with anything else than a class fails). So why isn’t B recognized as a class in the previous situation ?