I think the author is specifically talking about those cases where performance really matters. You could still have callback hell, but a lot less so.

As an aside, there is an alternative: passing a default value. This is Swift syntax:

  let favoriteIceCream = [
      "Paul": "Chocolate",
      "Sophie": "Vanilla"
  ]
  let result = favoriteIceCream["Charlotte", default: "Unknown"]