From: Robert Dober <robert.dober@...>
Date: 2008-04-06T04:55:52+09:00
Subject: Re: The ||= assignment operator

On Sat, Apr 5, 2008 at 7:57 PM, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
> David A. Black wrote:
>
>
> > The only time this matters is with hashes that have default values. In
> > every other case, as far as I know, x = x || y also describes what's
> > happening. But the expansion which describes *every* case is x || x =
> > y.
> >
>
>  One other case (a very similar one) in which it matters is this:
>
>   class C
>     def x; @x || 5; end
>     def x=(v); puts "assigning @x=#{v}"; @x = v; end
>   end
>
>   c = C.new
>   c.x ||= 3 # no effect
>   p c.x     # 5
>   c.x = 2   # assigning @x=2
>   p c.x     # 2
>
>  --
>       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407
>
>
Hmm I am not sure I believe you rushed your example a little bit

c.x = c.x || a
and
c.x || c.x = a
seem to me having the same effect.

I only came up with a perverse example to show the difference
    class C
     count = 0
     def x; true end
     define_method :x= do |_|
       count += 1
       @x = count
     end
  end

  c = C.new
  c.x || c.x = 42
  p c
  c.x = c.x || 42
  p c
  c.x ||= 42
  p c

Cheers
Robert



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---
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