From: ara.t.howard@...
Date: 2006-01-20T06:12:22+09:00
Subject: Re: Dynamic class instantiation

On Fri, 20 Jan 2006, Jason wrote:

> Hi all,
>
> I have a situation where I need to dynamically execute an object from a
> String name. I read in pickaxe that as long as a capitalize the class
> name in the string, Ruby will see it as a Constant and thusly allow me
> to use it.
>
> For example:
>
> module Test
>
>  class MyClass
>     def do_something
>       puts "Something done."
>     end
>  end
>
> end
>
> (caller code)
>
> cls = "Test::MyClass"
> require cls
> obj = cls.new
> obj.do_something
>
> ------
>
> When I execute the above caller code, I get an error saying
>
> undefined method `new' for "Test::MyClass":String (NoMethodError)
>
> So, obviously, Ruby is telling me that there is no new method for the
> String "Test::MyClass". I'm trying to instantiate the class this way as
> I have specific methods that return object besides String, so I'm
> guessing eval(cls) isn't appropriate for me. Also, I checked the
> archives on the list with no luck.
>
> Any suggestions?
>
> Thx,


     def klass_stamp(hierachy, *a, &b)
       ancestors = hierachy.split(%r/::/)
       parent = Object
       while((child = ancestors.shift))
         klass = parent.const_get child
         parent = klass
       end
       klass::new(*a, &b)
     end


     class A; class B;end; end

     klass_stamp 'A::B'

hth.

-a
-- 
strong and healthy, who thinks of sickness until it strikes like lightning?
preoccupied with the world, who thinks of death, until it arrives like
thunder?  -- milarepa