title: Must child classes implement protocols to which their parents conform?
body: <p>I have a class, <code>MyClass</code>, which implements the <code>NSCopying</code> protocol, and I have a class, <code>MyClassChild</code>, which inherits from <code>MyClass</code>. <code>MyClassChild</code> does not implement the <code>NSCopying</code> protocol. The textbook I am reading says it must, however I can build successfully! Is the textbook wrong?</p>
  
  <pre><code>@interface MyClass : NSObject &lt;NSCopying&gt; {
  
  }
  
  @end
  
  @implementation MyClass
  
  -(id)copyWithZone:(NSZone *)zone
  {
      return self;
  }
  
  @end
  
  @interface MyClassChild : MyClass {
  
  }
  
  @end
  
  @implementation MyClassChild
  
  @end
  </code></pre>