pull.rb

# DoSomething has dependency on Configuration and pulls default from Configuration
#
module MyThingy
  class DoSomething
    def call(input, suffix = nil)
      input + (suffix || default_suffix)
    end
    
    private
    
    def default_suffix
      MyThing.configuration.default_suffix
    end
  end
  
  def configuration
    @configuration ||= Configuration.new
  end
  
  class Configuration
    attr_accessor :default_suffix
    
    def default_suffix
      @default_suffix ||= "_world"
    end
  end
end

push.rb

# Configuration has dependency on DoSomething and pushes default to DoSomething
#
module MyThingy
  class DoSomething
    def call(input, suffix = nil)
      input + (suffix || default_suffix)
    end
    
    class << self
      attr_accessor :default_suffix
    end
    
    private
    
    def default_suffix
      self.class.default_suffix || '_world'
    end
  end
  
  def configuration
    @configuration ||= Configuration.new
  end
  
  class Configuration
    attr_accessor :default_suffix
    
    def default_suffix=(new_suffix)
      DoSomething.default_suffix = new_suffix
    end
  end
end

usage.rb

MyThingy.configuration.default_suffix = '_planet'

command = MyThing::DoSomething.new
command.call("mars") # => "mars_planet"