From: Robert Klemme <shortcutter@...>
Date: 2006-12-24T01:15:05+09:00
Subject: Re: Help with a ruby idiom

On 23.12.2006 17:02, Tim Waters wrote:
> From the O'Reilly Cookbook there is code that keeps call functions in a
> hash as a subscriber/listener type pattern.  What I don't understand (or
> I don't understand how it works is the line:
> (@EventDispatcher_listeners[event] ||= []) << callback

a ||= b

is equivalent to

a || (a = b)

IOW

a = b unless a

IOW

unless a
   a = b
end

IOW

"eval b and assign the result to a if a is nil or false".

In this case, since a Hash is also involved the lengthy form looks like 
this:

unless @EventDispatcher_listeners[event]
   @EventDispatcher_listeners[event] = []
end
@EventDispatcher_listeners[event] << callback

I hope you admit that ||= is much more concise and elegant. :-)

HTH

	robert