From: Yukihiro Matsumoto <matz@...>
Date: 2009-08-27T08:11:51+09:00
Subject: Re: ||= with 1.8 and 1.9 ?

Hi,

In message "Re: ||= with 1.8 and 1.9 ?"
    on Thu, 27 Aug 2009 06:23:01 +0900, "David A. Black" <dblack@rubypal.com> writes:

|> 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

Basically, "var op= expr" works like "var = var op expr" but left hand
side expression (var) is evaluated only once.  For ||=, it is same as

  x = (x || y)

but

  x || (x = y)

is semantically same (well, almost).

							matz.