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

/// the corresponding key-value pair as a non-optional tuple.
///
///     print(imagePaths[glyphIndex!])
///     // Prints "("star", "/glyphs/star.png")"
///
/// A dictionary's indices stay valid across additions to the dictionary as
/// long as the dictionary has enough capacity to store the added values

  ///         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
