Question

Possible Duplicate:
undef – Why would you want to undefine a method in ruby?

Can anyone lay out a practical use for undef in ruby? I’m coming from languages like javascript and python that don’t have it built in. You could of course simulate it in a language like javascript:

var obj = { func:function(){alert("works")} }
obj.func() // -> "works"
delete(obj["func"])
obj.func() //->obj.func() is not a function

but I’ve never really had use for that. Are there some common situations where undef is actually useful?

EDIT —
Just came across this in the book “The Ruby Programming Language”:

Another technique to prevent copying
of objects is to use undef to simply
remove the clone and dup methods. Yet
another approach is to redefine the
clone and dup methods so that they
raise an exception with an error
message that specifically says that
copies are not permitted. Such an
error message might be helpful to
programmers who are using your class.

Answer 1

I can only say that I’ve never had a use for it in 5 years. Perhaps more usefully, grepping through the entire source of rails shows only 7 instances and they’re all meta-programming related. (undef_method has rather more instances at 22). It appears to be useful for testing the behaviour of classes with and without modules mixed-in.

Hopefully someone can point out some more conventional uses for it.

EDIT
See this previous question: undef – Why would you want to undefine a method in ruby?