From: dblack@...
Date: 2007-02-17T05:05:19+09:00
Subject: Re: Oppinions on RCR for dup on immutable classes

Hi --

On Sat, 17 Feb 2007, ara.t.howard@noaa.gov wrote:

> On Sat, 17 Feb 2007 dblack@wobblini.net wrote:
>
>> You could conceivably have a case where an object can't be dup'd, but is
>> mutable, like a singleton class.  If dup returns self, then you could end 
>> up
>> changing the object when you didn't want to.  It's probably not an everyday
>> problem... but I still don't like the idea of having to remember that "dup"
>> means "dup or self".
>
>
> you already do though?
>
>
>
> harp:~ > cat a.rb
> #
> # crappy
> #
>  h = { :point => 'we already have' }
>
>  h2 = h.dup
>
>  h2[:point] << ' that problem'
>
>  p h[:point]
> #
> # crappy
> #
>  h = { :point => 'we already have' }
>
>  h2 = h.clone
>
>  h2[:point] << ' that problem'
>
>  p h[:point]
> #
> # sledge hammer
> #
>  h = { :point => 'an imperfect solution' }
>
>  mcp = lambda{|obj| Marshal.load(Marshal.dump(obj))}
>
>  h2 = mcp[ h ]
>
>  h2[:point] << ' is to use marshal'
>
>  p h[:point]
>
>
> harp:~ > ruby a.rb
> "we already have that problem"
> "we already have that problem"
> "an imperfect solution"

I don't consider returning a shallow copy the same as returning self.
It's not the same object as the receiver of the "dup" message.


David

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