From: Wilson Bilkovich <wilsonb@...>
Date: 2005-08-16T05:51:09+09:00
Subject: Re: Mixing Constants into objects

On 8/15/05, Caleb Clausen <vikkous@gmail.com> wrote:
> On 8/14/05, David A. Black <dblack@wobblini.net> wrote:
> > On Mon, 15 Aug 2005, gabriele renzi wrote:
> > > mh.. maybe "lexical" is the better word ?
> >
> > I think it's more than that.  What I should have said was: constant
> > references are resolved at parse-time, rather than run-time.  At least
> > I think that's the case.
> 
> Just how constant lookups work is something of a mystery to me in some
> cases... it's clearly less dynamic than method lookup, but it is
> run-time lookup, not compile time:
> 
> irb(main):001:0> class K
> irb(main):002:1> Foo=1
> irb(main):003:1> end
> => 1
> irb(main):004:0> def fk; K::Foo end
> => nil
> irb(main):005:0> fk
> => 1
> irb(main):006:0> class K
> irb(main):007:1> Foo=2
> irb(main):008:1> end
> (irb):7: warning: already initialized constant Foo
> => 2
> irb(main):009:0> fk
> => 2

My (possibly totally off-base) understanding is that, as there is no
'compile' step in Ruby, the constants get 'burned' into the AST, as do
things like regular expression literals, between forward-slashes. 
That would explain why they "look" like runtime evaluations, but they
aren't the same kind of citizen as variables.