From: Tom Pollard <tomp@...>
Date: 2006-11-13T04:58:00+09:00
Subject: Re: Help convert a Perl user to the Ruby Way.


On Nov 12, 2006, at 2:40 PM, Paul Lutus wrote:
> Let's say we have an instance variable named "hash" that we are not  
> sure has
> been initialized at runtime, and we want to create a new hash where  
> there
> is none, but only then. Add this line:
>
> hash ||= {}
>
> Means "if 'hash' is a hash, do nothing, otherwise create a hash".

Strictly speaking, doesn't it mean "if 'hash' is nil (or false),  
assign to a newly created empty hash"?  You're not testing whether  
it's actually a hash already.  Also, maybe it's worth reminding the  
OP that an empty hash is not treated as 'false' in a logical  
expression in Ruby, as it would be in Perl.  So, if you were to  
repeatedly evaluate

     hash ||= {}

you'd only create a new Hash the first time.  In Perl, on the other  
hand, repeatedly evaluating the similar expression

     $hashref ||= {}

would create and assign a new hash repeatedly, until some hash  
element was assigned.

Tom