From: Robert Dober <robert.dober@...>
Date: 2007-02-18T08:29:36+09:00
Subject: Re: Oppinions on RCR for dup on immutable classes

On 2/17/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
> Hi --
>
> On Sun, 18 Feb 2007, Robert Dober wrote:
>
> > On 2/17/07, Dean Wampler <deanwampler@gmail.com> wrote:
> >>
> >> As someone else commented, perhaps the real issue is that
> >> 5.respond_to?(:dup) returns true yet 5.dup raises, so you have no way
> >> of knowing in advance that you shouldn't call dup.
> > That just came up recently and I agree that this is kind of inelegant
> > (euphemistically)
> > Maybe that would be a reasonable CR?
>
> See Ara's answer to Dean, though.  respond_to? isn't designed to tell
> you what will happen when you call the method.  Lots of objects
> respond to methods by raising exceptions.
>
> Maybe the reason people don't like dup doing that is that it *always*
> does it for some classes of object.  But I think that's in order to
> leave no mysteries.  dup is "advertised", so to speak, as something
> that every object can do.  So when an object can't do it, it's more
> gracious to explain why not (in the exception message).
>
> It's a lot like this:
>
>    irb(main):001:0> (0..10).to_a
>    => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>    irb(main):002:0> (0.0..10.0).to_a
>    TypeError: can't iterate from Float
>
> Ranges with floats in them could just undef to_a and not respond, but
> the expectation exists that all ranges have some meaningful
> relationship to the process of being converted into an array
> (including the relationship of opting out of it but in a way that
> tells you what's going on).
>
> I realize that two ranges are of the same class while, say, a string
> and nil aren't.  But it's not a class thing; it's more about
> collective (not necessary along class lines) behaviors and
> expectations.
Very well put David. I can only agree, it is better behavior.
Sorry Ara if I missed that post of yours this thread is a little bit complex.
R.
>
>
> David
>
> --
> Q. What is THE Ruby book for Rails developers?
> A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
>     (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
> Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
> A. Ruby Power and Light, LLC (http://www.rubypal.com)
>
>


-- 
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In fact, in some ways, we are more confused than ever.
But we feel we are confused on a higher level and about more important things.
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