   ///     let data = ["a": "1", "b": "three", "c": "///4///"]
   ///
   ///     let m: [String: Int?] = data.mapValues { str in Int(str) }
-  ///     // ["a": 1, "b": nil, "c": nil]
+  ///     // ["a": Optional(1), "b": nil, "c": nil]
   ///
   ///     let c: [String: Int] = data.compactMapValues { str in Int(str) }
   ///     // ["a": 1]

  ///         print("Response \(code): \(message)")
  ///     }
  ///     // Prints "Response 200: OK"
  ///     // Prints "Response 403: Access Forbidden"
  ///     // Prints "Response 301: Unknown response"
  ///
  /// When a dictionary's `Value` type has value semantics, you can use this

  ///     let message = "Hello, Elle!"
  ///     var letterCounts: [Character: Int] = [:]
  ///     for letter in message {
  ///         letterCounts[letter, default: 0] += 1
  ///     }
  ///     // letterCounts == ["H": 1, "e": 2, "l": 4, "o": 1, ...]
  ///
