From: Rick DeNatale <rick.denatale@...>
Date: 2009-05-06T10:31:53+09:00
Subject: Re: '=||'

On Tue, May 5, 2009 at 8:45 PM, Eleanor McHugh
<eleanor@games-with-brains.com> wrote:
> On 6 May 2009, at 00:09, 7stud -- wrote:
>>
>> Eleanor McHugh wrote:
>>>
>>> Are you referring to ||= ? If so it's one of the augmented assignment
>>> operators so you won't find it documented separately as it's syntactic
>>> sugar for:
>>>
>>> x = x || some_other_value
>>
>> Nope.
...
>> The statement:
>>
>> x ||= val
>>
>> is actually equivalent to:
>>
>> x = val unless x
>
>
> It seems you've misunderstood what happens under the hood when using
> augmented assignment with tables as '||=' then becomes syntactic sugar for
> 'x[] = x[] || some_other_value' and the assignment is performed via '[]='
> rather than '='. '[]=' will not create a key if it believes it already
> exists and this is the cause of the behaviour you're seeing.

No, if x is truthy then

  x ||= expression

will NOT do any assignment.

The real equivalent to x ||= y

is

x || x = y

The assignment is short-circuited.

For the proof see:

http://talklikeaduck.denhaven2.com/2008/04/26/x-y-redux


-- 
Rick DeNatale

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