From: dblack@...
Date: 2003-09-22T19:48:53+09:00
Subject: Re: Operator overloading

Hi --

On Mon, 22 Sep 2003, Tom Felker wrote:

> On Sun, 21 Sep 2003 11:29:27 -0700, dhtapp wrote:
>
> > Hi,
> >
> > I'm pretty new to Ruby, so someone may step in quickly to correct me.  But
> > my understanding is that, for any of the standard dyadic operators (+, -,
> > etc.) the shorthand
> >
> > j += 1
> >
> > is expanded before evaluation to:
> >
> > j = j + 1
>
> Not quite - I think j += 1 only evaluates j once.  I recall one instance
> where that helped me, performance-wise.

The j on the left isn't being evaluated; it's just being assigned to.
So in cases with objects that can have more than one instance (like
String), you get a new object:

  irb(main):001:0> j = "abc"
  => "abc"
  irb(main):002:0> j.id
  => 537889088
  irb(main):003:0> j += "d"
  => "abcd"
  irb(main):004:0> j.id
  => 537881918

With integers you don't, of course, but it's also a case of assigning
to a variable, where the variable name on the left just serves to
accept the assignment (in the expanded form).


David

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