title: The final word on NSStrings: Mutable and Immutable
body: <p>I've read in several books... and online... about immutable and mutable strings.
  They claim "immutable strings" can't be changed.
  (But they never define "change".)</p>
  
  <p>Which of these NSStrings could be changed without using NSMutableString?</p>
  
  <p>The string contains "catfish"... and I later try to change it to "cat".
  (Same letters, just shorter.)</p>
  
  <p>It contains "cat"... and I try to change it to "catfish".
  (Similar start... but just made longer.)</p>
  
  <p>I change "cat" into "CAT".
  (Same letters, but just the case has changed.)</p>
  
  <p>I change "cat" into "dog".
  (Totally different string, but the same length.)</p>
  
  <p>I change "cat" into "dogwood".
  (Totally different string, but longer.)</p>