Ruby service locator proposal. The irb.rb file defines 2 services (first and second) and leverages them in the Domain class.

irb.rb

require 'service_locator'

# Declare our services
Services.instance.config do
  service :first, "this is"
  service :second, " a test"
end

# See that ServiceDependent has convenience methods defined to access services.
puts ServiceDependent.instance_methods

# See that you can access services directly through the Services singleton.
Services.instance.service[:foo]
Services.instance.service[:bar]

# Define a domain class that is ServiceDependent and leverages the service
# accessor convenience methods to perform business ops.
class Domain
  include ServiceDependent

  def a_business_operation
    first + second
  end
end

# See that the business op succeeds.
domain = Domain.new
domain.a_business_operation

service_locator.rb

require 'singleton'


module ServiceDependent
end

class Services
  include Singleton

  attr_reader :services

  def initialize
    @services = {}
  end

  def service(key, svc=nil)
    if svc.nil?
      @services[key.to_sym]
    else
      @services[key.to_sym] = svc
    end
  end

  def config(&block)
    # Provides access to service method in configuration block.
    self.instance_exec &block

    # for each mapped service, define a convenience method in ServiceDependent to access it.
    @services.each do |sym, svc|
      ServiceDependent.send(:define_method, sym) { Services.instance.services[sym] }
    end
  end
end