From: "David A. Black" <dblack@...>
Date: 2008-04-06T05:02:57+09:00
Subject: Re: The ||= assignment operator

Hi --

On Sun, 6 Apr 2008, Robert Dober wrote:

> On Sat, Apr 5, 2008 at 7:57 PM, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
>> David A. Black wrote:
>>
>>
>>> The only time this matters is with hashes that have default values. In
>>> every other case, as far as I know, x = x || y also describes what's
>>> happening. But the expansion which describes *every* case is x || x =
>>> y.
>>>
>>
>>  One other case (a very similar one) in which it matters is this:
>>
>>   class C
>>     def x; @x || 5; end
>>     def x=(v); puts "assigning @x=#{v}"; @x = v; end
>>   end
>>
>>   c = C.new
>>   c.x ||= 3 # no effect
>>   p c.x     # 5
>>   c.x = 2   # assigning @x=2
>>   p c.x     # 2
>>
>>  --
>>       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407
>>
>>
> Hmm I am not sure I believe you rushed your example a little bit
>
> c.x = c.x || a
> and
> c.x || c.x = a
> seem to me having the same effect.

I don't think so:

irb(main):017:0> c = C.new
=> #<C:0x87d0c>
irb(main):018:0> c.x || c.x = 1    # 5 || c.x = 1  =>  5
=> 5
irb(main):019:0> c.instance_eval { @x }
=> nil
irb(main):020:0> c.x = c.x || 1    # c.x = 5 || 1  =>  c.x = 5
assigning @x=5
=> 5
irb(main):021:0> c.instance_eval { @x }
=> 5


David

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