From: Logan Capaldo <logancapaldo@...>
Date: 2006-09-11T23:25:29+09:00
Subject: Re: Constant lookup starting in superclass, not derived class

On Mon, Sep 11, 2006 at 09:59:21PM +0900, Chris Roos wrote:
> I'm no doubt missing something obvious but I found this a little
> confusing.  I would have expected the constant lookup to start in Bar
> and therefore succeed.  Instead, it appears to start in Base where Foo
> is not defined.
> 
> class Base
>  def foo
>    p Foo
>  end
> end
> 
> class Bar < Base
>  class Foo
>  end
> end
> 
> Bar.new.foo
> # ~> -:3:in `foo': uninitialized constant Base::Foo (NameError)
> # ~> 	from -:12
> 
> Can anyone explain what is happening please?
Constants, unlike methods and instance variables, are "quasi"-lexicaly
scoped. (I say "quasi" because a sub class can assign to a constant
without munging its parent class's constant) One way of getting around
this particular situation is to use #const_get. e.g.:

class Base
  def foo
    p self.class.const_get('Foo')
  end
end