From: James Edward Gray II <james@...>
Date: 2007-02-08T22:06:25+09:00
Subject: Re: access to constants from instance_eval

On Feb 8, 2007, at 5:46 AM, David Chelimsky wrote:

> Hi all,
>
> It seems that Ruby won't allow me to directly access class constants
> from instance_eval:
>
> irb(main):001:0> class Foo
> irb(main):002:1>   BAR = "bar"
> irb(main):003:1>   def bar
> irb(main):004:2>     BAR
> irb(main):005:2>   end
> irb(main):006:1> end
> => nil
> irb(main):007:0> foo = Foo.new
> => #<Foo:0x10d97f0>
> irb(main):008:0> foo.class.constants
> => ["BAR"]
> irb(main):009:0> foo.bar
> => "bar"
> irb(main):010:0> foo.instance_eval { bar }
> => "bar"
> irb(main):011:0> foo.instance_eval { BAR }
> NameError: uninitialized constant BAR
>        from (irb):11
>        from (irb):11:in `instance_eval'
>        from (irb):11
>
> Can anybody explain to me why this might be the case (is there a
> philosophical reason that this is correct?) and/or some meta-magic
> spell I can use to coerce instance_eval into recognizing foo's
> constants?

I doubt this is what you are after, but:

 >> class Foo
 >>   BAR = "bar"
 >>   def bar
 >>     BAR
 >>   end
 >> end
=> nil
 >> foo = Foo.new
=> #<Foo:0x11004cc>
 >> foo.instance_eval { self.class.const_get(:BAR) }
=> "bar"

James Edward Gray II