self.rb

# An Instructor represents a single instructor
class Instructor
  attr_reader :donut_count
  def initialize
    @donut_count = 0
  end

  def eat_donut
    @donut_count += 1
  end
end

# An InstructorTeam represents a collection of instructors
class InstructorTeam
  attr_reader :instructors
  def initialize
    @instructors = []
  end

  def add
    @instructors << Instructor.new
  end

  def bring_in_donuts
    @instructors.each do |instructor|
      rand(3).times do
        instructor.eat_donut
      end
    end
  end
end

liberal_arts_dept = InstructorTeam.new
6.times do |i|
  liberal_arts_dept.add
end

puts "#{liberal_arts_dept.instructors.length} liberal arts teachers"
# => 6 liberal arts teachers

science_dept = InstructorTeam.new
10.times do
  science_dept.add
end

puts "#{science_dept.instructors.length} science teachers"
# => 10 science teachers


# An alternate (and arguably less good) way of organizing
# things is to store the collection in a class variable
class Student
  @@all_students = []
  def initialize
    # Whenever a new instance is created, it is
    # automatically added to the collection
    # Note the use of self to reference the current object
    @@all_students << self
  end

  # Need an accessor method here because attr_reader
  # doesn't work for class variables
  def self.all_students
    return @@all_students
  end
end

24.times do
  Student.new
end

puts "#{Student.all_students.length} students"
# => 24 students

# The reason this technique is not recommended is because we're
# limited to one collection of students. If we wanted to split
# students out into cohorts, we'd have to do a bunch of redesign.

# In essence, the Student class is responsible for two things:
# keeping track of a single student and keeping track of the
# set of all students. Better to separate this out into two classes.