From: Eric Mahurin <eric_mahurin@...>
Date: 2005-05-01T12:17:03+09:00
Subject: Re: Cloning into an object

--- Robert Klemme <bob.news@gmx.net> wrote:
> 
> "George Ogata" <g_ogata@optushome.com.au> schrieb im
> Newsbeitrag 
> news:87zmvfx6u9.fsf@optushome.com.au...
> > Eric Mahurin <eric_mahurin@yahoo.com> writes:
> >
> >> Anybody know how to generically copy (shallow like clone)
> an
> >> object into another object?  It would be nice to handle
> the
> >> case where the objects have a different class, but I would
> at
> >> least like to know how to do it when the classes are the
> same.
> >>
> >> Here is an example of what I would like to do:
> >>
> >> dest = Object.new # or String.new if necessary
> >> source = "hello world"
> >> destid = dest.id
> >>
> >> source.clone_into(dest)
> >>
> >> dest             -> "hello world"
> >> dest.id==destid  -> true
> >> dest.class       -> String
> >
> > I hear that evil.rb has Object#become, which will do that
> with some
> > caveats.  Search "Object#become" in the list archives for
> more info.
> 
> If you just want to copy state you can do without evil magic
> (although not 
> working for builtins like String, Array, Fixnum etc.):
> 
> class Object
>   def set_from(o)
>     o.instance_variables.each do |var|
>       instance_variable_set( var, o.instance_variable_get(
> var ) )
>     end
>     self
>   end
> end


Thanks for the pointers.  I downloaded evil.rb and tried
"become" (used dest.become(source) for the copy) and it did
exactly what I wanted.

I read a little more about become.  It looks like it might be
made standard in ruby at some point.  Will it have the above
functionality.  Or will it do something like what I think the
smalltalk "become" does - change all references to the
destination object to point to the source object.  I really
don't want the reference changes because a) it seems very
expensive (search the object space), and b) this would cause
the object id to change.

Anybody know when/if become will be made standard?


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