Understanding the BOOS, "Don't ask tell" from a talk at GORUCO 2012

teaching_myself_boos_tda.rb

## 
# Growing Object Oriented Software
# Tell, don't ask approach

# Tested and learned the principle

class SomeProgram
  def self.runit
    # Printer is the main purpose
    # Later I might want to Log, IM, Email or Ping something about the printing result.
    # So with this approach I can just add or remove any of either Logger, InstantMessenger, Mailer or Pinger
    printer = Printer.new(Mailer.new(Pinger.new(self)))
    printer.print!
  end
  
  def self.print_successful
    puts "#{self} finally got the message that print! was a success\n\n"
  end
end

class Printer < Struct.new(:listener)
  
  def print!
    puts "#{self.class} is printing something... \n\n"
    sleep 1
    puts "#{self.class} is now telling #{self.listener.class} that print! was successful\n\n"
    sleep 1
    listener.print_successful
  end
end

class Logger < Struct.new(:listener)
  
  def print_successful
    puts "#{self.class} was told to logg that print! was a success\n\n"
    sleep 1
    puts "#{self.class} is now telling #{self.listener.class} that print! was a success\n\n"
    sleep 1
    listener.print_successful
  end
end

class Mailer < Struct.new(:listener)
  
  def print_successful
    puts "#{self.class} was told to email that print! was a success\n\n"
    sleep 1
    puts "#{self.class} is now telling #{self.listener.class} that print! was a success\n\n"
    sleep 1
    listener.print_successful
  end
end

class InstantMessenger < Struct.new(:listener)
  
  def print_successful
    puts "#{self.class} was told to IM that print! was a success\n\n"
    sleep 1
    puts "#{self.class} is now telling #{self.listener.class} that print! was a success\n\n"
    sleep 1
    listener.print_successful
  end
end

class Pinger < Struct.new(:listener)
  
  def print_successful
    puts "#{self.class} was told to ping that print! was a success\n\n"
    sleep 1
    puts "#{self.class} is now telling #{self.listener.class} that print! was a success\n\n"
    sleep 1
    listener.print_successful
  end
end

SomeProgram.runit