From: "David A. Black" <dblack@...>
Date: 2007-10-18T10:39:42+09:00
Subject: Re: abstract superclasses

Hi --

On Thu, 18 Oct 2007, Yossef Mendelssohn wrote:

> ]On Oct 17, 2:41 pm, "Thomas Adam" <thomas.ada...@gmail.com> wrote:
>> On 17/10/2007, Giles Bowkett <gil...@gmail.com> wrote:
>>
>>> I sometimes use the Java thing of an abstract superclass in Ruby. I
>>> usually just set up the abstract parent so that it'll break if used
>>> directly. Is it better to just use Modules? Have other people run into
>>> this?
>>
>> I'd use a Module, yes.  Or a class:
>>
>> class SomeClassMimickingAbstract
>>         private_class_method :new
>> end
>>
>> But you don't need to think this way in Ruby -- unlike Java, Ruby is
>> weakly typed.
>>
>> -- Thomas Adam
>
> How do you suggest to use that class? I understanding keeping the
> "abstract" class from being instantiated, but what about the concrete
> classes, the ones you're going to use?
>
> class RealThing < SomeClassMimickingAbstract
>  # now make .new public again
> end
>
> Ugly, isn't it? Of course, that's just more fuel for the "don't do
> this in Ruby" fire.

You could do:

   class C
     private_class_method :new
     def self.inherited(c)
       class << c; public :new; end
     end
   end

I've actually never felt the need for abstract classes in Ruby
programs. I'm not a Java programmer, so it never would have occurred
to me in that context, and I haven't found myself inventing it for
Ruby.


David

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