From: dblack@...
Date: 2002-10-25T02:20:37+09:00
Subject: Re: Things That Newcomers to Ruby Should Know (10/16/02)

Hi --

On Fri, 25 Oct 2002, Austin Ziegler wrote:

> On Thu, 24 Oct 2002 20:21:54 +0900, dblack@candle.superlink.net
> wrote:
> > On Thu, 24 Oct 2002, William Djaja Tjokroaminata wrote:
> >> Therefore, a person with a C++ background, who is used to
> >> avoiding the creation of unnecessary intermediate objects, will
> >> be surprised that Ruby does it *all the time* in its '+='
> >> operator. (Furthermore, the creation of equivalent intermediate
> >> objects may even be more "expensive" in Ruby than in C++ in
> >> absolute terms.)
> > I don't think "a += 'str'" (or whatever) is creating an
> intermediate
> > object though, at least not in the sense that I understand the
> term.
> > It's just performing an assignment, not doing anything extra.
>
> It's creating an intermediate object that then becomes the original
> object, in a sense. I think that the C++ programmer -- where

I think that's kind of a roundabout way to describe it though.  I
would say: it's creating a new object, and assigning a reference to
that object to a variable which previously held a reference to a
different object.

> references are often used like "safe" or "pretty" pointers, would
> expect the following code to print out the same Object#ID both times
> -- and it doesn't. It doesn't because you're creating a composite
> object (a + "bar") and then making a refer to that object rather
> than the original a.

Right -- what I was saying was just that "intermediate object" didn't
sound like the right term to me, just as when you say:

  a = "Hello"

you're just creating an object (which I would not consider an
intermediate object).  I guess I think of intermediate object creation
as, for instance:

  a = [1,2,3]
  b = a.map {|x| x * 2} .map {|x| x * 3}

where there's an anonymous array being created en route to the
eventual creation of the array referred to by 'b'.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav