title: Assigning NSMutableString from NSString Warning
body: <p>I have the following three lines of code in my program:</p>
  
  <pre><code>NSMutableString *stringOne = [NSMutableString stringWithFormat:@"Hello "];
  NSMutableString *stringTwo = [NSMutableString stringWithFormat:@"World"];
  NSMutableString *sayIt = [stringOne stringByAppendingString:stringTwo];
  </code></pre>
  
  <p>Despite the fact that it works, the third line is causing the warning Assigning NSMutableString * from NSString *.</p>
  
  <p>I am at a loss here since everything I am using is an NSMutableString.</p>