From: dreamcat four <dreamcat4@...>
Date: 2009-10-12T04:34:51+09:00
Subject: Re: Class Level inheritable attributes - are we there yet?

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. 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"]

Most people would try / expect to fix by putting attr_accessor :foo at
top class A. It simply doesn't work and the regular accessor is not
inherited. Because in Ruby the Class is instantiated as an instance of
object. You could probably imagine a little imaginary OO professor
tugging at your clothes and saying 'tut tut, such a shame' or
something. And you might argue back that the point was that these
aren't bugs if you understand the limitations etc, etc. Just like
being back at school eh? But i can assure you when any real programmer
in the real world comes along to use your classes and / or modify your
code, these holes are eventually surface as real breakages / bugs.


Heres my own top 3 recommendations:

* Give up / don't use any. Avoid if possible.

* Use the activeresource class inheritable accessor. I guess that's
not so much of a stretch if you are already depending upon
activeresource for other things.

* Request a real language implementation in ruby core because class is
an object. It would be entirely a matter for the ruby development team
to decide whether they would want to implement it, and/or how. I'm
very surprised no-one has asked for this on 1.9 line, or to change the
existing @@ behaviour since are changed the block level variable
scoping and many other things.


dreamcat4
dreamcat4@gmail.com