From: Rick DeNatale <rick.denatale@...>
Date: 2009-05-06T22:59:33+09:00
Subject: Re: '=||'

On Wed, May 6, 2009 at 9:43 AM, Eleanor McHugh
<eleanor@games-with-brains.com> wrote:
> On 6 May 2009, at 13:03, Rick DeNatale wrote:
>>
>> The short circuiting only happens if the lhs expression returns a
>> non-truthy value.
>>
>> Now it's true (I think) that "a op= b" is the same as "a = a op b" in
>> C, Ruby ain't C.
>
> :)
>
>> Sometimes the stuff "under the hood" is a little more complicated than
>> it first appears. <G>
>
>
> Very true, and we all learn new stuff by considering it. For example I
> suspect quite a few people would be surprised by the following code:
>
> class Test
>  def initialize
>    @switch = false
>  end
>
>  def [] x
>    puts "[#{x}]"
>    @switch = !@switch
>  end
>
>  def []= x, y
>    puts "[#{x}] = #{y}"
>  end
> end
>
> t = Test.new
> t[:a] ||= 17
> t[:a] ||= 17
> t[:a] ||= 17
>
> output:                 [a]
>                                [a]
>                                [a]
>
> here the '[]' call returns 'true' and 'false' by turns but in either event
> the assignment fails to call '[]='...


Are you sure?  When I run your code I get this:

[a]
[a]
[a] = 17
[a]



-- 
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale