Observer Pattern

Author: peterstefanov

ObserverPattern/Observer.pdf

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+
+class Binary < Participant
+
+  def init_limits(lower, upper)
+    num = (lower+upper)/2
+  end
+
+  def do_play(lower, num, upper)
+    while ((result = @oracle.is_this_the_number?(num)) != :correct) && (@num_attempts <= @max_num_attempts) do
+      if result == :less_than
+        upper = num-1
+      elsif result == :greater_than
+        lower = num+1
+      end
+      num=init_limits(lower, upper)
+      @num_attempts+=1
+    end
+    notify_observers
+  end
+
+  def player_name
+    self.class.name
+  end
+end

ObserverPattern/binary.rb

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+
+class Linear < Participant
+
+  def init_limits(lower, upper)
+    num = lower
+  end
+
+  def do_play(lower, num, upper)
+    notify_observers
+    while @oracle.is_this_the_number?(num)!=:correct && (@num_attempts <= @max_num_attempts) do
+      num+=1
+      @num_attempts+=1
+    end
+  end
+
+  def player_name
+    self.class.name
+  end
+end

ObserverPattern/linear.rb

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+
+# Evaluate the performance of participants using different guessing strategies
+
+require_relative 'oracle.rb'
+require_relative 'participant.rb'
+require_relative 'random_.rb'
+require_relative 'linear.rb'
+require_relative 'smart_random.rb'
+require_relative 'binary.rb'
+require_relative 'play_game.rb'
+
+NUM_OF_RUNS = 8
+
+oracle = Oracle.new
+
+total_num_attempts = 0
+total_num_failures = 0
+
+players = Array.new
+
+random_player = Random_.new(1,NUM_OF_RUNS, oracle, max_num_attempts: NUM_OF_RUNS*2)
+random_player.add_observer do |player|
+  puts("#{player.player_name} finished the game and took him  #{player.num_attempts} to guess the number!")
+end
+
+linear_player = Linear.new(1,NUM_OF_RUNS, oracle, max_num_attempts:NUM_OF_RUNS*2)
+linear_player.add_observer do |player|
+  puts("#{player.player_name} is playing !")
+end
+
+smart_random_player = SmartRandom.new(1,NUM_OF_RUNS, oracle, max_num_attempts:NUM_OF_RUNS*5)
+smart_random_player.add_observer do |player|
+  puts("#{player.player_name} finished the game and took him  #{player.num_attempts} to guess the number!")
+end
+
+binary_player = Binary.new(1,NUM_OF_RUNS, oracle, max_num_attempts:NUM_OF_RUNS*5)
+binary_player.add_observer do |player|
+  puts("#{player.player_name} made an successful attempt and took him #{player.num_attempts}!")
+end
+
+players.push(PlayGame.new(random_player))
+players.push(PlayGame.new(linear_player))
+players.push(PlayGame.new(smart_random_player))
+players.push(PlayGame.new(binary_player))
+
+
+players.each { |player|
+  total_num_attempts = 0
+  total_num_failures = 0
+  1.upto(NUM_OF_RUNS) do |i|
+    oracle.secret_number = i
+    player.reset
+    if player.play==:success
+      total_num_attempts += player.num_attempts
+    else
+      total_num_failures += 1
+    end
+  end
+  player.delete_observer(player)
+
+  puts "Player with strategy #{player.player_name} took on average #{total_num_attempts/(NUM_OF_RUNS-total_num_failures)} attempts to succeed"
+}
+
+
+

ObserverPattern/main.rb

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+
+module ObservableSubject
+
+    def initialize
+      @observers=[]
+    end
+
+    def add_observer(&observer)
+      @observers.push(observer)
+    end
+
+    def delete_observer(observer)
+      puts("#{observer.player_name} has been deleted!")
+      @observers.delete(observer)
+    end
+
+    def notify_observers
+      @observers.each do |observer|
+        observer.call(self)
+      end
+    end
+
+end

ObserverPattern/observable_subject.rb

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+
+# Knows the number the participants are trying to guess
+class Oracle
+  attr_writer :secret_number
+
+  def initialize(secret_num:0)
+    @secret_number = secret_num
+  end
+
+  def is_this_the_number? num
+    if num == @secret_number
+      :correct
+    elsif num > @secret_number
+      :less_than
+    elsif num < @secret_number
+      :greater_than
+    end
+  end
+
+end

ObserverPattern/oracle.rb

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+
+require_relative 'oracle.rb'
+require_relative 'observable_subject.rb'
+
+# Tries to guess the 'secret' number using several different strategies
+class Participant
+  attr_accessor :num_attempts, :oracle
+  attr_reader :lower, :upper
+
+  include ObservableSubject
+
+  def initialize(lower, upper, oracle, max_num_attempts:10)
+    super()
+    @oracle, @max_num_attempts, @lower, @upper = oracle, max_num_attempts, lower, upper
+    @num_attempts = 0
+  end
+
+  #Template method
+  def play
+    num = init_limits(@lower, @upper)
+    @num_attempts+=1
+    do_play(@lower, num, @upper)
+    compare
+  end
+
+  def init_limits(lower, upper)
+    raise "Abstract method called"
+  end
+
+  def do_play(lower, num, upper)
+    raise "Abstract method called"
+  end
+
+  def compare
+    if (@num_attempts <= @max_num_attempts)
+      :success
+    else
+      fail
+    end
+  end
+
+
+  def reset
+    @num_attempts = 0
+  end
+
+  def player_name
+    self.class.name
+  end
+
+  private
+  def fail
+    :fail
+  end
+
+end

ObserverPattern/participant.rb

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+require 'rspec'
+require_relative 'participant'
+require_relative 'oracle'
+
+rand_values = [10, 7, 4, 9, 6, 5, 2, 8, 1, 3, 0] # for rand
+
+describe 'participant behaviour' do
+
+  before do
+    @oracle = Oracle.new(secret_num:4)
+    @participant = Participant.new(@oracle, max_num_attempts:5)
+    allow(Kernel).to receive(:rand).and_return(*rand_values) # mocking Kernel.rand
+  end
+
+  it 'guesses the number 4 in 3 attempts using play_randomly' do
+    expect(@participant.play(0, 10)).to eq(:success)
+    expect(@participant.num_attempts).to eq(3)
+  end
+
+  it 'guesses the number 4 in 5 attempts using play_linear' do
+    expect(@participant.play(0, 0)).to eq(:success)
+    expect(@participant.num_attempts).to eq(5)
+  end
+
+  it 'guesses the number 4 in 3 attempts using play_smart_random' do
+    expect(@participant.play(0, 10)).to eq(:success)
+    expect(@participant.num_attempts).to eq(3)
+  end
+
+  it 'guesses the number 4 in 4 attempts using play_binary_search' do
+    expect(@participant.play(0, 10)).to eq(:success)
+    expect(@participant.num_attempts).to eq(4)
+  end
+
+end

ObserverPattern/participant_spec.rb

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+require_relative 'observable_subject.rb'
+
+class PlayGame
+
+  include ObservableSubject
+
+  def initialize(player)
+    super()
+    @player = player
+  end
+
+  def play
+    @player.play
+  end
+
+  def reset
+    @player.reset
+  end
+
+  def num_attempts
+    @player.num_attempts
+  end
+
+  def player_name
+    @player.player_name
+  end
+end

ObserverPattern/play_game.rb

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+
+require_relative 'observable_subject.rb'
+
+class Random_ < Participant
+
+
+  def init_limits(lower, upper)
+    num = Kernel.rand(lower..upper)
+  end
+
+  def do_play(lower, num, upper)
+    while @oracle.is_this_the_number?(num)!=:correct && (@num_attempts <= @max_num_attempts) do
+      num = init_limits(lower, upper)
+      @num_attempts+=1
+    end
+    notify_observers
+  end
+
+  def player_name
+    self.class.name
+  end
+
+  def player_name
+    self.class.name
+  end
+end

ObserverPattern/random_.rb

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+
+class SmartRandom < Participant
+
+  def init_limits(lower, upper)
+    num = Kernel.rand(lower..upper)
+  end
+
+  def do_play(lower, num, upper)
+    while ((result = @oracle.is_this_the_number?(num)) != :correct) && (@num_attempts <= @max_num_attempts) do
+      if result == :less_than
+        upper = num-1
+      elsif result == :greater_than
+        lower = num+1
+      end
+      num = init_limits(lower, upper)
+      @num_attempts+=1
+    end
+    notify_observers
+  end
+
+  def player_name
+    self.class.name
+  end
+end