From: Joel VanderWerf <vjoel@...>
Date: 2007-05-19T03:12:37+09:00
Subject: Re: Constants Question

Peer Allan wrote:
> Hi,
> 
> I have building a small custom library and I want to be able to define a
> constant in each subclass identifying "valid" options.  Each subclass
> will have its own list.
> 
> here is how I tried to do it, please ignore the literal values, this is
> just an example:
> 
> class Base
>   def method(option)
>     raise MyException unless VALID.include?(option)
>     do_with_option(option)
>   end
> end
> 
> class SubClassA < Base
>   VALID = ['color','size','weight']
> end
> 
> class SubClass < Base
>   VALID = ['name','phone','email']
> end
> 
> sub = SubClass.new
> sub.option('phone')
> 
> This results in a "uninitialized constant VALID" error.  Why is that?
> It is like the VALID constant is not being recognized in the subclass.

Constants are statically scoped, so it really is unrecgnize in the 
context of Base.

Use this instead of VALID:

self.class::VALID

this forces dynamic lookup, and it will be found in the appropriate 
subclass.

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