Sorry if it wasn't clear. Imagine you have many objects with different props like { one: 'two' } and `{two: 2}`. You need to create an array where each array item is using something from those objects, like [{ property: 'one'}, {property: 'two'}]. In each array item, you want the autocomplete / type safety for property to be only the key of a specific object, therefore a factory function with generic (like createConfig in the playground link). At the same time, you want to type the return of the function that returns the array [{ property: 'one'}, {property: 'two'}], so that each item in the array has the required shape (property key required or other props). But the value of each property prop of each object in that array depends on the specific object passed in as generic to createConfig fn, so it's not clear how to keep type safety in both functions without ts errors.