From: Rein Henrichs <reinh@...>
Date: 2010-06-08T02:05:28+09:00
Subject: Re: Question about abbreviated indexing assignments

On 2010-06-07 08:42:08 -0700, J�rg W Mittag said:

> 	h[:key] ||= :value
> 	# "Setting key to value"
> 	h[:key] ||= :value
> 
> But this doesn't.
> 
> Since the purpose of the specification is to describe the currently
> existing implementations, this is obviously a bug in the specification
> rather than a bug in all five currently released implementations,
> especially since there is a ton of code and even a common idiom that
> depends on the current behavior. But what would the correct
> specification look like?
> 
> Thanks in advance,
>     J�rg.

It is commonly thought that x <operator>= y is exactly equivalent to x 
= x <operator> y in all cases. What you have just demonstrated is that, 
presumably for performance reasons, h[key] ||= value is in fact 
equivalent to h[key] || h[key] = value, rather than h[key] = h[key] || 
value. This prevents a second lookup in the case where k[key] exists 
and is not nil or false.

As to what the correct specification would look like, I am not sure, 
but I do agree with you.

-- 
Rein Henrichs
http://puppetlabs.com
http://reinh.com