From: Robert Klemme <shortcutter@...>
Date: 2009-10-12T18:14:17+09:00
Subject: Re: Class Level inheritable attributes - are we there yet?

2009/10/11 dreamcat four <dreamcat4@gmail.com>:
> On Sun, Oct 11, 2009 at 6:55 PM, Robert Klemme
> <shortcutter@googlemail.com> wrote:
>> Having said that I am not sure that you actually need a language construct
>> when you can do this:
>>
>>
>> class A
>>  class <<self
>>    def foo
>>      @foo || superclass.foo
>>    end
>>  end
>>
>
> It shouldn't be mandated to re-invent the wheel in any programming
> language, even if its fun style / fun to write.

Which wheel did I reinvent?

> Here is why Robert:
> because you would have just put 2 bugs into your code.
>
> 1) It breaks when you want to set foo = nil in a subclass.
> 2) Not having an accessor definition will break other code.
>
> puts A.instance_variables.inspect
> => ["@foo"]
> puts B.instance_variables.inspect
> => []
> puts C.instance_variables.inspect
> => ["@foo"]

David has said everything there is to say about this.  I modeled the
quick hack based on your original example which obviously needed to
maintain constant values at class level which would have been better
done like this:

11:07:12 desktop$ ruby19 cl.rb
A  1
B  1
C  2
11:07:24 desktop$ cat cl.rb
class A
  Foo = 1
end

class B < A
end

class C < A
  Foo = 2
end

[A,B,C].each do |cl|
 printf "%-2s %p\n", cl, cl::Foo
end

If any, that would have been the "bug" in my approach.  The code was
merely meant to demonstrate what can be done with a few lines of code
and that accessors (in fact all methods) defined for class instances
are inherited to subclasses.

Regards

robert

-- 
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