Polymorphism with different method signatures

I have a group of classes (say for validation rules). Each one returns a true or false.

I use id and call a method signature for each one of the classes and get the results allowing me to dynamically create validation rules.

Worked great until...

I have a new class that takes an extra parameter to come up with its validation.

What is the best way to deal with this?

Modify every other classes method signature to take a parameter that they don't need?

From stackoverflow Mel

• Probably the most appropriate course of action is to abstract your parameter passing into an object that can have a variable profile of variables.

  Of course, more simply, Objective-C does allow for a variable parameter list much like C:

  void method(int a, ...)     // in C
  - (void) method:(id) firstObject, ...  // in ObjC
  

  Apple has Technical Q&A on the very subject.

  Jon Reid : Yes, putting the variables into an NSDictionary would let the various classes pick & choose what they're interested in.
  From rcw3