Simple type inference for properties of an object

Inferable.ts

type Inferable<T, K extends keyof T> = T[K] extends Function ? T[K] : never;

function asInferable<T, K extends keyof T>(_: T, key: K): (fn: Inferable<T, K>) => void {
  return function(fn: Inferable<T, K>) {
    console.log(fn("world"));
  };
}

class Foo {
  bar(str: string): string {
    return `hello ${str}`;
  }
  baz(num: number): number {
    return 1 + num;
  }
}

asInferable(new Foo(), "qux")(() => {}); // Argument of type '"baz"' is not assignable to parameter of type '"bar"'
asInferable(new Foo(), "bar")(() => {}); // Argument of type '() => void' is not assignable to parameter of type '(str: string) => string'
asInferable(new Foo(), "bar")((num: number) => 1 + number); // Argument of type '(num: number) => number' is not assignable to parameter of type '(str: string) => string'
asInferable(new Foo(), "baz")((str: string) => `Hola! ${str}`); // Argument of type '(str: string) => string' is not assignable to parameter of type '(num: number) => number'
asInferable(new Foo(), "bar")((str: string) => `Hola! ${str}`); // Works 👍
asInferable(new Foo(), "bar")(() => `Hola!`); // Also Works 👍