From: "David A. Black" <dblack@...>
Date: 2008-01-16T07:43:06+09:00
Subject: Re: Why @hash ||= Hash.new in Set#initialize?

Hi --

On Wed, 16 Jan 2008, Kornelius Kalnbach wrote:

> David A. Black wrote:
>> I noticed this:
>>
>>   def initialize(enum = nil, &block)
>>     @hash ||= Hash.new
>> 
>> in set.rb. I'm wondering why the assignment is ||= rather than just =.
>> All the tests pass without the ||.
> I don't know...but maybe somebody wants to inherit from set, like this:
>
>  class MySet < Set
>    def initialize(*args, &block)
>      @hash = HashWithSpecialFeatures.new
>      super(*args, &block)
>    end
>  end
>
> In this case, @hash wouldn't be overwritten.

I guess it would have that effect, but I've seen lots of instance
variable initialization in classes that might be subclassed, and I
don't remember ever seeing a conditional one.


David

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