composite.rb

#!/usr/bin/env ruby
# conding: utf-8

class Task
  attr_reader :name

  def initialize(name)
    @name = name
  end

  def get_time_required
    0.0
  end
end

class CompositeTask < Task

  def initialize(name)
    super(name)
    @sub_tasks = []
  end

  def add_sub_task(task)
    @sub_tasks << task
  end

  def remove_sub_task(task)
    @sub_tasks.delete(task)
  end

  def get_time_required
    time = 0.0
    @sub_tasks.each {|task| time += task.get_time_required}
    time
  end
end

class AddATask < Task
  
  def initialize
    super('AddATask')
  end

  def get_time_required
    1.0
  end
end

class AddBTask < Task
  
  def initialize
    super('AddBTask')
  end

  def get_time_required
    1.0
  end
end

class MixTask < CompositeTask

  def initialize
    super('MixTask')
    add_sub_task(AddATask.new)
    add_sub_task(AddBTask.new)
  end

end

mixTask = MixTask.new
p mixTask.get_time_required