From: Eric Mahurin <eric_mahurin@...>
Date: 2005-05-10T03:09:13+09:00
Subject: Re: RCR 304: reference/pointer concept

Here are a couple of things this might be useful for (I just
put these in the RCR).  I'm sorry I didn't provide something
more concrete sooner.  Regarding #2, I've used references to
hash values many times to get better efficiency (in perl). 
i.e.

$a = \$hash{$key}
# read and modify $$a

Doing this, only one lookup is needed (for making the ref) as
opposed to 2 (for the get and set).  As far as I know, we can't
get this extra efficiency for hash values in Ruby.  You can
create references to hash values in my Ruby implementation, but
it doesn't give you any additional efficiency.  That would need
to be done at the C level.  And that would be useful -
especially for large hashes.


1. pass-by-reference or pass an lvalue. From what I understand,
the way you would write/use a Ruby method that modified lvalues
right now, would be like this:

 def byvalue(*args)
     # read and modify args
     args
 end
 a,b,c = *byvalue(a,b,c)

With references, you could do this:

 def byref(*args)
     # read and modify args[i][]
 end
 byref(ref{:a},ref{:b},ref{:c})

With this simple variable case, there isn't much advantage, but
when you are dealing with something deep within an object, it
can offer an advantage:

 a["hi"][3],io.pos = *byvalue(a["hi"][3],io.pos)

vs.

 byref(a["hi"].ref[3],io.ref.pos)

Also, with the byvalue case, you are forced into the assign,
whereas byref may choose not to do this assign. Depending on
the object, this could even prevent an exception (i.e.
IO#pos=).

2. Although not addressed in this implementation, a reference
could provide some efficiency when ther is some work that could
be saved when you get or set the same thing 2 or more times.  A
primary example of this would be a reference to a hash value. 
With a good implementation of a reference to a hash value, you
would only need to do the hash lookup once (while making the
reference).  Compare this to what you have now - you do a hash
lookup every time you get/set a given hash value.

--- Bill Atkins <batkins57@gmail.com> wrote:
> What would this accomplish?
> 
> On 5/9/05, Eric Mahurin <eric_mahurin@yahoo.com> wrote:
> > I just submitted RCR 304 with the rubyforge 'reference'
> > project/gem implementation:
> > 
> > http://www.rcrchive.net/rcr/show/304
> > 
> > Go vote and make comments on it!
> > 
> > Discover Yahoo!
> > Use Yahoo! to plan a weekend, have fun online and more.
> Check it out!
> > http://discover.yahoo.com/
> > 
> > 
> 
> 
> -- 
> Bill Atkins
> 
> 


		
__________________________________ 
Yahoo! Mail Mobile 
Take Yahoo! Mail with you! Check email on your mobile phone. 
http://mobile.yahoo.com/learn/mail