On 28 Apr '08, at 5:00 PM, K. Darcy Otto wrote:
I need to have a subclass optionally extend a method already in the superclass. After some research, my best guess is that an optionally defined protocol is the best way to go about this.
If you really want a fully abstract method, use a category:
@interface ClassA : NSObject
{
...
}
...
@end
@interface ClassA(Check)
-(BOOL)optionalMethodToImplement;
@end
Now you don't have to implement that method in the base class, but the
compiler will allow you to call it on any instance of ClassA. (Of
course at runtime you'll get a message-not-understood exception if the
subclass didn't implement the method.)
To see if an instance implements that method, call [self respondsToSelector: @selector(optionalMethodToImplement:)].
if ([self conformsToProtocol:@protocol(Check)])
[self optionalMethodToImplement];
}
Problem #1: The compiler complains that ClassA may not respond to
optionalMethodToImplement.
If you still want to do it this way, you can work around that problem by casting the receiver:
[(id<Check>)self optionalMethodToImplement];
—Jens
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