From: Robert Klemme <bob.news@...>
Date: 2005-07-07T16:40:47+09:00
Subject: Re: Inheriting Array and slice() behaviour

Patrick Gundlach wrote:
> [...]
>
>>   OTOH, inheriting classes like Array is seldom really good.
>> There are too many methods that return plain arrays and you end up
>> with Arrays anyway.  Delegation, ad hoc modification or extension
>> with a Module is often better.
>
> Now it is the second time I've read this. Currently I have a class
> that stores an 8 bit encoding. The elements of this class are accessed
> directly just like an array. So now I have
>
> class ENC < Array
>
>   attr_accessor :foo
>
>   def initialize(fileobject=nil)
>      # if fileobject then initialize 256 elements with the contents
>      # of the file
>      # else
>      #  super(256,"undefined slot")
>   end
>   def somefunction
>     # read the contents of the 256 and store the result of
>     # some operation in @foo
>   end
> end
>
> So I get [], []= and a lot of things for free. My subclass is basicly
> an array with some additional methods attached. What do you suggest
> instead? Something like
>
> class ENC < DelegateClass(Array)
>   ...
> end

Yep.  Or do it selectively (what I'd prefer).  This can help:

class Module
  def delegate(member, method)
    class_eval "def #{method}(*a,&b) @#{member}.#{method}(*a,&b) end"
  end
end

>> class Foo
>>   def initialize() @s = "foo" end
>>
?>   delegate :s, :size
>> end
"def size(*a,&b) @s.size(*a,&b) end"
=> nil
>> Foo.new.size
=> 3

Btw, IMHO this would be a good addition to delegate.rb.  What do others
think?

Kind regards

    robert