From: Marcello Barnaba <bofh@...>
Date: 2007-02-18T21:54:43+09:00
Subject: Re: Oppinions on RCR for dup on immutable classes

Hi,

On Sunday 18 February 2007 13:16, SonOfLilit wrote:
> Say, why not just define Object#mutable? and solve the issue of not
> knowing if dup is possible or not?

In my opinion, this exposes at the ruby level an implementation detail that 
pollutes the language design, and you must add it to the "weird things you 
should remember".

Please, compare

def a
  obj = some_method
  raise 'hey!' unless obj.mutable?
  do_stuff obj.dup
rescue SomeMethodError
  pull_out_the_power_cord
end

to

def a
  do_stuff some_method.dup
rescue SomeMethodError
  pull_out_the_power_cord
rescue TypeError
  raise 'hey!'
end

I think that the whole design is clear and makes sense, you can call a method, 
and you should catch exceptions, if you care about them. Or let them stop 
execution, if needed.

> Sure, it only works to tell you about one possible reason it's not,
> but it seems like a good workaround, far better than, say, duping just
> to check.

Why should "dup" behave differently than all the other methods that raise 
exceptions when something exceptional happens? :)

my 0.02c
-- 
pub 1024D/8D2787EF  723C 7CA3 3C19 2ACE  6E20 9CC1 9956 EB3C 8D27 87EF