title: nsarray using Key-Value Collection Operators
body: <p>I'm just learning about <a href="https://developer.apple.com/library/ios/#documentation/cocoa/conceptual/KeyValueCoding/Articles/CollectionOperators.html" rel="nofollow noreferrer">Collection Operators</a> and my first example isn't working. How can I fix this?</p>
  
  <pre><code>NSArray *arr = [NSArray arrayWithObjects:[NSNumber numberWithInt:1], 
                  [NSNumber numberWithInt:10], 
                  [NSNumber numberWithInt:100], 
                  [NSNumber numberWithInt:1000], 
                  nil];
  NSLog(@"%@", [arr valueForKeyPath:@"@min"]);
  </code></pre>
  
  <p>I crash out with:</p>
  
  <blockquote>
    <p>this class is not key value coding-compliant for the key min</p>
  </blockquote>