[ruby-core:17884] Re: duping the NilClass

David A. Black wrote (and Shohei Urabe supported):
> Hi --
>
> On Mon, 21 Jul 2008, Nasir Khan wrote:
>
>> I write a lot of hand crafted dup or clone because I want control as
>> well as
>> better performance than the Marshal idiom. I ended up re-opening
>> NilClass,
>> TrueClass and FalseClass for def dup; self; end
>> While most of the things in Ruby are very intuitive and predictable from
>> functional perspective, this sort of stood out.. that's all.
>
> I understand not wanting true.dup etc. to break things,

So you agree that the current behavior just breaks things?

Or do you (or somebody else) know about something that would be
broken by changing the behavior (i.e. returning self)?


> but it's hard
> for me to get past the fact that true.dup doesn't return a dup of
> true, if it's defined to return true.

There are objects where a dup returns a true duplicate,
and there are some special ones where you can duplicate
and duplicate and it's still the same. Sometimes the
laws of physics (or computation) are not exactly what
they seem to be. There are some objects that you can
duplicate and duplicate, and they just stay the same :-).

Given duck typing and all, returning itself (the truest
of true copies, so to say) seems to be the best behavior
for dup on these objects.

>Maybe it's a case for a
> "dangerous" dup:
>
>   class Object
>     def dup!
>       dup
>     rescue TypeError
>       self
>     end
>   end

In what sense would this definition of dup(!) be dangerous?

I think I understand your analogy with other ! methods, giving
back the same object instead of a new one, but ! methods are
used when something is being changed, and the objects in
question are characterized just by the fact that they can't
be changed, so ! doesn't seem very appropriate.

(Of course, because we are using Ruby, nil and friends *can*
be changed, but that's not something one would usually do,
and is independent of the issue at hand.)

Regards,    Martin.



#-#-#  Martin J. Du"rst, Assoc. Professor, Aoyama Gakuin University
#-#-#  http://www.sw.it.aoyama.ac.jp       mailto:[e-mail]