From: ale@...
Date: 2001-01-27T09:13:21+09:00
Subject: [ruby-talk:9967] Re: Dynamically instantiating a class (with a string)

On Sat, 27 Jan 2001, Phil Tomson wrote:

> I know I could (and probably should) do this with some kind of a factory
> pattern...
> 
> In Perl I can instantiate an object using a string that contains the name
> of that object, like so:
> 
> 
> $PLATFROM = "PC";
> $myPCTool = "Tool$PLATFORM"->new(blah...);
> #later:
> $PLATFORM = "UNIX";
> $myUnixTool = "Tool$PLATFORM"->new(blah...);
> #where I have a class called ToolPC and another called ToolUNIX which
> #inherit from Tool.
> 
> I kind of like this capability, is there any way to do something like that
> in Ruby?

Hello Phil,

I'd like to leave you with Dave's answer, but I don't like eval too
much. So here's a way to find a class (searches breadth-first).

There has been discussions about this before at ruby-talk (IIRC), but I
was unable to find them with blade. Maybe someone can point our earlier
discussions.

   - Aleksi

module Kernel
  def get_class_for_name(name, objects = [Object])
    return nil if objects.size == 0
    object = objects.shift
    object.constants.each do |constant_name|
      real_object = object.const_get(constant_name)
      case real_object
      when Class
	return real_object if constant_name == name
      when Module
	objects << real_object
      end
    end
    return get_class_for_name(name, objects)
  end
end

klass = get_class_for_name("Fixnum")
puts "#{klass} of type #{klass.type}"

module Foo
  module Bar
    class Zak
    end
  end
end

klass = get_class_for_name("Zak")
puts "#{klass} of type #{klass.type}"

class ToolPC
  def identity
    puts "PC would suck, but luckily it runs unix"
  end
end

class ToolUNIX
  def identity
    puts "how come POSIX was never based on DOS?"
  end
end

for platform in ["PC", "UNIX"]
  myTool = get_class_for_name("Tool"+platform).new
  myTool.identity
end