From: dblack@...
Date: 2006-09-23T17:24:00+09:00
Subject: Re: How do I instantiate a class who's name is dynamic?

Hi --

On Sat, 23 Sep 2006, Ben Harper wrote:

> I want to do the following, where 'somefile' is a dynamic value:
> require 'somefile.rb'
> 'somefile.rb' will have a module inside it named "Magic_Module_somefile"
> Inside that module there will be a class named "Magic_Class_somefile"
> How do I new() that class ?

You can get at it using const_get.  Here's an irb demo:

irb(main):001:0> s = "somefile"
=> "somefile"
irb(main):002:0> module MM_somefile; class MC_somefile; end; end
=> nil
irb(main):003:0> Object.const_get("MM_#{s}").const_get("MC_#{s}").new
=> #<MM_somefile::MC_somefile:0xb7f85c34>

It's also possible to write a const_get variant that handles the ::
separator automatically:

   class Object
     def const_get_recursive(const)
       const.split("::").inject(Object) {|c1,c2| c1.const_get(c2)}
     end
   end

   const_get_recursive("MM_#{s}::MC::#{s}").new


David

-- 
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org