or other.rb

# Not exactly sure what I'm doing here...
class RestKlass
  %W[get post put delete].each { |verb|
    define_method(verb) { |res| res }
  }

  def get; :gotten end
end

class SQLKlass
  %W[select insert update delete].each { |verb|
    define_method(verb) { |res| res }
  }

  def select; :selected end
end

class HasManyProtocols
  # an object representing a duck type that can be used in a case expression
  class Protocol
    def initialize(*selectors)
      @selectors = selectors
    end

    def ===(object)
      @selectors.all? {|selector| object.respond_to?(selector)}
    end
  end

  REST = Protocol.new(:get, :post, :put, :delete)
  SQL =  Protocol.new(:select, :insert, :update, :delete)

  attr_reader :obj

  def initialize(obj)
    @obj = obj
  end

  def result(*args)
    case obj
    when REST then RestKlass.new
    when SQL  then SQLKlass.new
    end
  end
end

require 'spec'

TEST_CASE = proc do |klass|
  proc do
    it "finds restful object" do
      klass.new(RestKlass.new).result.get.should == :gotten
    end

    it "finds sql object" do
      klass.new(SQLKlass.new).result.select.should == :selected
    end
  end
end

# A DSLy approach to the above..
class HasManyOtherwise
  def self.handlers
    @handlers ||= {}
  end

  def self.handle(name, *args)
    handlers[name] = args
  end

  handle RestKlass, :get, :post, :put, :delete
  handle SQLKlass, :select, :insert, :update, :delete

  def initialize(obj)
    @obj = obj
  end

  def result
    HasManyOtherwise.handlers.detect { |key,val|
      val.all? { |sym| @obj.respond_to?(sym) }
    }[0].new
  end
end

describe HasManyProtocols, &TEST_CASE[HasManyProtocols]
describe HasManyOtherwise, &TEST_CASE[HasManyOtherwise]