From: Peter Zotov <whitequark@...>
Date: 2012-04-21T21:39:35+09:00
Subject: Re: What does '||=' mean?

Ian M. Asaff писал 21.04.2012 05:20:
> equivalent to
>
> @ivar = @ivar || value
>
> ruby || short circuits, so if @ivar is nil, then value gets assigned 
> to
> @ivar. it's referred to as a "nil guard".
>
> see http://forums.pragprog.com/forums/130/topics/3644

The info on that link is incorrect or outdated. On recent Rubies like 
1.9.3
the nil guard explicitly does not show a warning if the variable did 
not exist
beforehand. Check it yourself:

$ ruby -W2 -e '@ivar ||= 1'
$ ruby -W2 -e '@ivar = @ivar || 1'
-e:1: warning: instance variable @ivar not initialized

>
> On Fri, Apr 20, 2012 at 9:15 PM, Soichi Ishida <lists@ruby-forum.com> 
> wrote:
>
>> Well, as stated in the subject, what does '||=' mean?
>>
>> It's from
>>
>>  def current_cart
>>    if session[:cart_id]
>>      @current_cart ||= Cart.find(session[:cart_id])  #HERE!!!
>>      session[:cart_id] = nil if @current_cart.purchased_at
>>    end
>>    if session[:cart_id].nil?
>>      @current_cart = Cart.create!
>>      session[:cart_id] = @current_cart.id
>>    end
>>    @current_cart
>>  end
>>
>> Is this Rails issue? I thought it's some Ruby grammar thing, because 
>> I
>> know there is an expression, '|='.
>>
>> Thanks in advance.
>>
>>
>> soichi
>>
>> --
>> Posted via http://www.ruby-forum.com/.
>>
>>

-- 
   WBR, Peter Zotov.