From: Thomas Wieczorek <wieczo.yo@...>
Date: 2008-03-03T17:54:49+09:00
Subject: Re: Understanding ruby classes

You can use Object.const_get(klass) to get the Class class of every
defined Ruby class(in your scope).
Try this:

class MyPrint
    def printHDR
        raise NotImplementedError
    end
end

class MyPrint2HTML
    def printHDR
        puts "I am HTML"
    end
end

class MyPrint2PDF
    def printHDR
        puts "I am PDF"
    end
end

class MyPrintFactory
    def self.getPrinter(options = {})
       printer = nil
       if options.empty? || !options.key?(:format)
            raise ArgumentError.new("no Printer Format given")
       else
            begin
                printer = Object.const_get("MyPrint2" +
options[:format].upcase).new
            rescue NameError => ex
                raise ArgumentError.new("Unknown Format")
            end
       end

       return printer
    end
end
printer = MyPrintFactory.getPrinter :format => 'html'
printer.printHDR
printer = MyPrintFactory.getPrinter :format => 'pdf'
printer.printHDR
printer = MyPrintFactory.getPrinter :format => 'doc'
printer.printHDR