From: Jeff Rose <rosejn@...>
Date: 2006-05-23T01:15:11+09:00
Subject: Re: initializing instance variables in a module

That's what I was afraid of.  In this example case it's no big deal, but 
in a module where you are accessing a more complex variable many times 
it's a real pain, let alone inefficient.  We are working on an event 
system, so the hash is a hash of arrays or possibly a hash of hashes. 
Any of 4 methods could be called, which would require an initialized 
value.  Having this in every method is sorta lame...

   handlers = (@event_handlers ||= Hash.new {|k,v| k[v] = []})[key]

Of course we can pull it out to a method:

def handlers(key)
   @event_handlers ||= Hash.new {|k,v| k[v] = []})[key]
end

  but just initializing on inclusion seems to be the most reasonable 
way, doesn't it?

-Jeff

Ryan Leavengood wrote:
> module Foo
>   def add_stuff(key, stuff)
>     (@foo_the_stuff ||= {})[key] = stuff
>   end
> end
> 
> If @foo_the_stuff is null, it will be initialized to an empty hash,
> otherwise the existing value will be used. I consider this use of ||=
> to be a Ruby idiom.
> 
> Ryan
> 
> On 5/22/06, Jeff Rose <rosejn@gmail.com> wrote:
>> Have a module:
>>
>> Module Foo
>>    def add_stuff(key, stuff)
>>      @foo_the_stuff[key] = stuff
>>    end
>> end
>>
>> class Bar
>>    include Foo
>> end
>>
>> Is there a standard or correct way to initialize @foo_the_stuff in this
>> example?  Should the add_stuff method check whether the variable has
>> been initialized every time, or should this be done by implementing a
>> callback like append_features or included?  (That's how I'd want to do
>> it, but it's not clear which or how...)
>>
>> Thanks,
>> Jeff
> 
>