From: ara.t.howard@...
Date: 2006-09-21T02:19:23+09:00
Subject: Re: const_defined? not quite in sync with const_get ??

On Thu, 21 Sep 2006, Chris Roos wrote:

> Assuming the following snippet, I'd expect Foo::const_defined?(:Bar)
> to be routed via Foo::const_missing.  Instead it resolves to top-level
> Bar.  Can someone explain why please?
>
> --code--
>
> class Bar
> end
>
> module Foo
> def self.const_missing(konst)
>   puts "missing konst #{konst}"
> end
> end
>
> Foo::Bar
> #=> missing konst Bar # Unsurprising behaviour
>
> p Foo::const_defined?(:Bar)
> false # Unsurprising behaviour
>
> p Foo::const_get(:Bar)
> #=> Bar # Surprising behaviour
>
> --/code--
>
> Cheers,
>
> Chris

non-prefixed constants follow the normal scoping rules:

harp:~ > cat a.rb
class Bar
end

module Foo
   def self.const_missing(konst)
     puts "missing konst #{konst}"
   end
end

Foo::Bar
#=> missing konst Bar # Unsurprising behaviour

p Foo::const_defined?('Bar')
false # Unsurprising behaviour

p Foo::const_get('Foo::Bar')
#                 ^^^^^
#                 ^^^^^
#                 ^^^^^
#=> Bar # Surprising behaviour


harp:~ > ruby a.rb
missing konst Bar
false
a.rb:16:in `const_get': wrong constant name Foo::Bar (NameError)
         from a.rb:16


-a
-- 
in order to be effective truth must penetrate like an arrow - and that is
likely to hurt. -- wei wu wei