Open Radar

 
Overriding a superclass' method or implementing a protocol with optional methods can result in subtle bugs, including:

* Accidentally overriding a superclass' method.
* Misspelling a superclass' method, thus not actually overriding it.
* Misspelling an optional protocol method, thus not actually implementing it.

Java provides an '@override' annotation to handle these cases:

  <http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Override.html>

And C# provides an 'override' keyword:

  <http://msdn.microsoft.com/en-us/library/ebca9ah3.aspx>
  <http://msdn.microsoft.com/en-us/vcsharp/aa336813.aspx>

A similar keyword in Objective-C, like @override, could work the same way:

@override
-(void)drawRect:(NSRect)rect
{
}

If you mark a method with @override, it *must* be declared in either the superclass or an optional protocol method.  If not, you get a compiler error (or maybe just a warning).

Perhaps an @implement keyword could be used for protocols since you aren't strictly overriding anything:

@implement
- (NSInteger)numberOfRowsInTableView:(NSTableView *)tableView
{
}

This may be polluting keywords too much, and @override could be used for both cases, even if it's not strictly correct for protocols.