From: timr <timrandg@...>
Date: 2009-11-20T16:00:05+09:00
Subject: Re: eval behaves differently inside a method definition...

> The parent class effectively acts as a namespace for the subclass. BTW, I really don't think I should call it a "subclass", as that seems to imply inheritence - none of that here. Maybe someone else can tell us the proper name for this structure/pattern.
>

I understand--how about nested class or encapsulated class.

> So you probably understand the issue by now, eval within the String class (whether or not inside a method definition) creates a "subclass" of sorts, and hence you can't call it directly outside. If you tried to call "String::Pumpkin.new" instead after using your "irb" method, it would have worked (try it out). Alternately, you could have done it this way:
>
> class String
> def irb
> eval self
> end
> end
> "class ::Pumpkin;def pie;puts 'yum';end;end".irb
> Pumpkin.new.pie
>
> Hope that helps.
> - Ehsan
>

Ehsan, nice explanation!
Hmmm. That means that you could make a binding to main
>> SPECIAL_BINDING = binding
and add that to the eval argument to get it back to the main scope
where eval seems to work on anything:

class String
def irb
eval(self, SPECIAL_BINDING)
end
end

Now it should all work!
>> "puts 'yohoo'"
=> "puts 'yohoo'"
>> "puts 'yohoo'".irb
yohoo
=> nil
>> "class What;def cool;puts 'is totally awesome';end;end".irb
=> nil
>> What.new
=> #<What:0x1032a7c>
>> What.new.cool
is totally awesome
=> nil
>>

Mucho Gracias, amigo!!!
Tim