From: Colin Bartlett <colinb2r@...>
Date: 2010-01-19T01:54:57+09:00
Subject: Re: what does this mean?

On Mon, Jan 18, 2010 at 3:44 AM, Ruby Newbee <rubynewbee@gmail.com> wrote:
> For this statement:
>   @speaks_english ||= @name.size > 6
> does it mean something like below?
>   if @name.size > 6
>      @speaks_english ||= @name.size
>   end

As an addition to the other replies to your question, there is a useful
post on this by Rick DeNatale, see below.
Rick DeNatale also notes that x &&= y behaves similarly - it means:
  x && (x = y)

I've emphasized the last sentence below because although
I know the real meaning of ||= the point that it preserves
the short-circuit nature hadn't occurred to me, and I think
it's a useful help to remembering exactly what ||= does.

http://talklikeaduck.denhaven2.com/2008/04/26/x-y-redux

A while back there was quite a thread on the Ruby-lang mailing list
about the real semantics of the expression.
  a[x] ||= some_value
In many books and articles on Ruby the form:
  a <op>= b
Where <op> is an operator like + is described as syntactic sugar for:
  a = a <op> b
While this is true in most cases, it isn't true if the operator is ||.
...
Matz explains that the real expansion of x ||= y is:
  x || (x = y)
...
Since || is a ‘short-circuit’ boolean operator,
the left hand operand expression is only evaluated
if the right hand operand expression evaluates
to a logically false value, i.e. either nil or false.

The way that Matz included ||= as an assignment operator
makes perfect sense to me. *** The ||= assignment operator
reserves the short-circuit nature of ||. ***