map.swift

let dict = [1:"a", 2:"b"]
let key: Int? = 2
if let value = key.map({ dict[$0] }) {
  print(value) // "Optional("b")"
}
if let key = key, value = dict[key] {
  print(value) // "b"
}
if let value = key.flatMap({dict[$0]}) {
  print(value) // "b"
}