From: brabuhr@...
Date: 2009-08-27T07:03:24+09:00
Subject: Re: ||= with 1.8 and 1.9 ?

On Wed, Aug 26, 2009 at 5:23 PM, David A. Black<dblack@rubypal.com> wrote:
> Hi --
>
> On Thu, 27 Aug 2009, brabuhr@gmail.com wrote:
>> According the rubyspec project:
>>
>>  language/variables_spec.rb:
>>   describe "Operator assignment 'var op= expr'" do
>>     it "is equivalent to 'var = var op expr'" do
>
> It isn't, though, at least in the ||= case (see Joel W.'s post).
> Matz's characterization of it to me at RubyConf (or somewhere) was:
>
>  x ||= y   same as    x || x = y

Yeah, that version matches my mental model.

x ||= y
    x = x || y
    x || x = y

x += y
    x = x + y
    x + x = y # :-)

o.x ||= y
    o.x = o.x || y
      # .x= is always called
    o.x || o.x = y
      # .x= is not always called

o.x += y
    o.x = o.x + y

Then maybe ||= and += should be split apart in rubyspec:
  describe "var += expr" it "is equivalent to 'var = var op expr'"
  describe "var ||= expr" it "is equivalent to 'var || var = expr'"