From: Joel VanderWerf <vjoel@...>
Date: 2006-10-26T14:39:17+09:00
Subject: Re: Popularity Contest: Initializing Class-Level Instance Variables

Phrogz wrote:
> TECHNIQUE 2 - ON-DEMAND TEST/INITIALIZATION
> -------------------------------------------
> class Alpha
>   def self.m1; (@foo||=[]) << rand; end
>   def self.m2; (@foo||=[]).map{ rand }; end
> end
> 
> class Bravo < Alpha
>   # Nothing special here
> end

I prefer a variant of the above:

class Alpha
   def foo
     @foo ||= []
   end
   def self.m1; foo << rand; end
   def self.m2; foo.map{ rand }; end
   # note that the expression for contstructing foo is not
   #  repeated twice
end

class Bravo < Alpha
   # Nothing special here
end

class Charlie < Alpha
   def foo
     @foo ||= Set.new # or some other collection class
   end
   # This implies that all _subclasses_ of Charlie will
   # (unless overridden) use a set for the #foo method
end

class Delta < Charlie
   # default to Charlie's choice of Set as the foo collection
end

class Echo < Alpha
   def initialize(*)
     super
     @foo = [1,2,3] # possible to specify in advance
   end
end

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407