struct Programmer {
  let brain: Brain
  let laptop: Laptop?
  let name: String
}
struct Brain {
}
struct Laptop {
  let name: String
  let fan: Fan?
}
struct Fan {
  let name: String
}

let programmer = Programmer(brain: Brain(), laptop: nil, name: "Ramu")
let laptop = Laptop(name: "mac", fan: Fan(name: "mac fan"))
let programmerWithLaptop = Programmer(brain: Brain(), laptop: laptop, name: "Somu")

// Let's say we want to get the name of the programmer's laptop
// and also the name of the fan in laptop
// Note: Fan is also optional for a laptop
// How will we do it using if-let ?
var laptopName: String?     // by default, laptopName(optional) will take `nil` value.
var laptopFanName: String?
if let laptop = programmer.laptop {
  laptopName = laptop.name
  if let fan = laptop.fan {
     laptopFanName = fan.name
  }
}