Examples of Patterns in Ruby
- Adapter
- Builder
- Command
- Composite
- Decorator
- Facade
- Factory
- Interpreter
- Iterator
- Observer
- Proxy
- Singleton
- State
- Strategy
- Template
- Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.[link]
class Quest
attr_accessor :difficulty, :hero
def initialize(difficulty)
@difficulty = difficulty
@hero = nil
end
def finish
@hero.exp += calculate_experience
end
def calculate_experience
@difficulty * 50 / @hero.level
end
end
class Hero
attr_accessor :level, :exp, :quests
def initialize
@level = 1
@exp = 0
@quests = []
end
def take_quest(quest)
@quests << (quest.hero = self)
end
def finish_quest(quest)
quest.finish
@quests.delete quest
end
end
class OldQuest
attr_accessor :hero, :difficulty, :experience
def initialize
@difficulty = 3
@experience = 10
end
def done
difficulty * experience
end
end
class QuestAdapter
attr_accessor :hero
def initialize(old_quest, difficulty)
@old_quest = old_quest
@old_quest.difficulty = difficulty
@hero = nil
end
def finish
@hero.exp += @old_quest.done
end
end
# Usage
hero = Hero.new
quest = Quest.new 5
hero.take_quest quest
hero.finish_quest quest
puts hero.exp
# => 250
some_old_quest = OldQuest.new
old_quest_adapted = QuestAdapter.new(some_old_quest, 5)
hero.take_quest old_quest_adapted
hero.finish_quest old_quest_adapted
puts hero.exp
# => 300- Separate the construction of a complex object from its representation so that the same construction process can create different representations.[link]
class BoardBuilder
def initialize(width, height)
@board = Board.new
@board.width = width
@board.height = height
@board.tiles = []
@board.monsters = []
end
def add_tiles(n)
n.times{ @board.tiles << Tile.new }
end
def add_monsters(n)
n.times{ @board.monsters << Monster.new }
end
def board
@board
end
end
class Board
attr_accessor :width, :height, :tiles, :monsters
def initialize
end
end
class Tile; end
class Monster; end
# Usage
builder = BoardBuilder.new 2, 3
puts builder.board
# => Board Object
board = builder.board
puts board.width
# => 2
builder.add_tiles(3)
builder.add_monsters(2)
puts board.tiles.size
# => 3
puts board.monsters.size
# => 2- Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.[link]
class Turn
def initialize
@commands = []
end
def run_command(command)
command.execute
@commands << command
end
def undo_command
@commands.pop.unexecute
end
end
class Hero
attr_accessor :money, :health
def initialize
@money = 0
@health = 100
end
end
class GetMoneyCommand
def initialize(hero)
@hero = hero
end
def execute
@hero.money += 10
end
def unexecute
@hero.money -= 10
end
end
class HealCommand
def initialize(hero)
@hero = hero
end
def execute
@hero.health += 10
end
def unexecute
@hero.health -= 10
end
end
# Usage
hero = Hero.new
get_money = GetMoneyCommand.new hero
heal = HealCommand.new hero
turn = Turn.new
turn.run_command(heal)
puts hero.health
# => 110
turn.run_command(get_money)
puts hero.money
# => 10
turn.undo_command
puts hero.money
# => 0- Composition over inheritance. Compose objects into tree structures to represent part-whole hierarchies.[link]
class CompositeQuest
def initialize
@tasks = []
end
def <<(task)
@tasks << task
end
def reward
@tasks.inject(0){ |sum, task| sum += task.reward }
end
end
class MegaQuest < CompositeQuest
end
class Quest < CompositeQuest
end
class MonsterTask
attr_reader :reward
def initialize
@reward = 100
end
end
class PuzzleTask
attr_reader :reward
def initialize
@reward = 200
end
end
# Usage
quest1 = Quest.new
quest1 << MonsterTask.new
quest1 << PuzzleTask.new
puts quest1.reward
# => 300
quest2 = Quest.new
quest2 << MonsterTask.new
quest2 << PuzzleTask.new
megaquest = MegaQuest.new
megaquest << quest1
megaquest << quest2
puts megaquest.reward
# => 600- Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.[link]
class ItemDecorator
def initialize(item)
@item = item
end
# this needs to be delegated with other efective way
def use
@item.use
end
end
class MagicItemDecorator < ItemDecorator
def price
@item.price * 3
end
def description
@item.description + "Magic"
end
end
class MasterpieceItemDecorator < ItemDecorator
def price
@item.price * 2
end
def description
@item.description + "Masterpiece"
end
end
class Item
attr_reader :price, :description
def initialize
@price = 10
@description = "Item "
end
def use
"do something"
end
end
# Usage
item = Item.new
magic_item = MagicItemDecorator.new(item)
puts magic_item.price
# => 30
puts magic_item.description
# => Item Magic
masterpiece_item = MasterpieceItemDecorator.new(item)
puts masterpiece_item.price
# => 20
puts masterpiece_item.description
# => Item Masterpiece
# all next lines puts "do something"
item.use
magic_item.use
masterpiece_item.use- The goal of the Facade Pattern is to provide a unified interface to a set of interfaces in a subsystem. This means you'd just have some object that can send back other objects.[link]
class Hero
attr_reader :name
def initialize(name)
@name = name
end
def join(level)
puts "#{self.name} join #{level}\n"
end
def attack(enemy)
puts "#{self.name} kick #{enemy}\n"
end
end
class Enemy
attr_reader :name
def initialize(name)
@name = name
end
def dead(hero)
puts "#{self.name} killed by #{hero}"
end
end
class Level
attr_reader :stage
def initialize(stage)
@stage = stage
end
def to_s
stage
end
end
class GameFacade
attr_reader :hero, :enemy, :level
def initialize
@hero = Hero.new('Sonic')
@enemy = Enemy.new('Eggman')
@level = Level.new('Green Hill')
end
def start_game
hero.join(level)
hero.attack(enemy.name)
enemy.dead(hero.name)
end
end
game = GameFacade.new
game.start_game
# => Sonic join Green Hill
# Sonic kick Eggman
# Eggman killed by Sonic- Define an interface for creating an object, but let subclasses decide which class to instantiate.[link]
class Party
attr_reader :members
def initialize(factory)
@members = []
@factory = factory
end
def add_warriors(n)
n.times{ @members << @factory.create_warrior }
end
def add_mages(n)
n.times{ @members << @factory.create_mage }
end
end
class HeroFactory
def create_warrior
Warrior.new
end
def create_mage
Mage.new
end
end
class Hero
def initialize
end
end
class Warrior < Hero
end
class Mage < Hero
end
# Usage
party = Party.new(HeroFactory.new)
party.add_warriors(3)
party.add_mages(2)
puts party.members.size
# => 5
puts party.members.count{ |member| member.class == "Mage" }
# => 2- This pattern provides an interpreter to deal with an abstract language. Using classes we can understand the inputs for parse them.[link]
class Word
def initialize(value)
@value = value
end
def execute
@value
end
end
class Plus
def initialize(first, second)
@first = first
@second = second
end
def execute
@first.execute + @second.execute
end
end
class Minus
def initialize(first, second)
@first = first
@second = second
end
def execute
index = @first.execute =~ /#{@second.execute}/
second_index = index + @second.execute.length
@first.execute[0,index] + @first.execute[second_index..-1]
end
end
class Interpreter
def self.parse(input)
@waiting_second_word = false
words = []
operations = []
input.split.each_with_index do |value|
if value =~ /^[^+-].*/ && !@waiting_second_word
words << Word.new(value)
else
if symbol = operations.pop()
first = words.size > 1 ? Word.new(words.map(&:execute).join(" ")) :
words.pop
second = Word.new(value)
case symbol
when /\A\+/
words << Word.new(Plus.new(first, second).execute)
when /\A\-/
words << Word.new(Minus.new(first, second).execute)
end
@waiting_second_word = false
else
@waiting_second_word = true
operations << value
end
end
end
words.pop.execute
end
end
puts Interpreter.parse("NA + NA + NA + BATMAN")
#=> NANANABATMAN
puts Interpreter.parse("you know nothing Jon Snow - nothing")
#=> you know Jon Snow
puts Interpreter.parse("hello + world - llowo")
#=>herld- Iterator helps you to iterate through a complex object using an iterator method.[link]
class Parent
attr_reader :first_name
def initialize(first_name, gender)
@first_name = first_name
@gender = gender
end
end
class Child < Parent
end
class Family
def initialize(surname)
@surname = surname
@children = []
end
def add_father(first_name)
@father = Parent.new first_name, "M"
end
def add_mother(first_name)
@mother = Parent.new first_name, "F"
end
def add_child(first_name, gender)
@children << Child.new(first_name, gender)
end
def each_member
[@father, @mother, @children].flatten.each do |member|
yield member
end
end
end
# Usage
family = Family.new "Jackson"
family.add_father("Robert")
family.add_mother("Susan")
family.add_child("Lucas", "M")
family.add_child("James", "M")
family.add_child("Rose", "F")
family.each_member{ |member| puts member.first_name }
# => Robert
# Susan
# Lucas
# James
# Rose- Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.[link]
module Observable
attr_reader :observers
def initialize(attrs = {})
@observers = []
end
def add_observer(observer)
@observers << observer
end
def notify_observers
@observers.each{ |observer| observer.update }
end
end
class Tile
include Observable
def initialize(attrs = {})
super
@cursed = attrs.fetch(:cursed, false)
end
def cursed?
@cursed
end
def activate_curse
notify_observers
end
end
class Hero
attr_reader :health
def initialize
@cursed = false
@health = 10
end
def damage(hit)
@health -= hit
end
def cursed?
@cursed
end
def discover(tile)
if tile.cursed?
@cursed = true
tile.add_observer(self)
end
end
def update
damage(4)
end
end
# Usage
hero = Hero.new
tile = Tile.new cursed: true
hero.discover(tile)
tile.activate_curse
puts hero.health
# => 6
puts hero.cursed?
# => true- Provide a surrogate or placeholder for another object to control access to it.[link]
require 'forwardable'
class Hero
attr_accessor :keywords
def initialize
@keywords = []
end
end
class ComputerProxy
# Forwardable allows objects to run methods on behalf
# of it's members, in this case the Computer object
extend Forwardable
# We delegate the ComputerProxy's use of
# the Computer object's add method
def_delegators :real_object, :add
def initialize(hero)
@hero = hero
end
def execute
check_access
real_object.execute
end
def check_access
unless @hero.keywords.include?(:computer)
raise "You have no access"
end
end
def real_object
@real_object ||= Computer.new
end
end
class Computer
def initialize
@queue = []
end
def add(command)
@queue << command
end
def execute
"executing commands"
end
end
# Usage
hero = Hero.new
proxy = ComputerProxy.new(hero)
proxy.add("some command")
proxy.execute
# => raise error
hero.keywords << :computer
proxy.execute
# => executing commands- Define a unique instance of an object.[link]
class HeroFactory
@@instance = nil
def self.instance
@@instance ||= HeroFactory.send(:new)
end
def create_warrior
Warrior.new
end
def create_mage
Mage.new
end
private_class_method :new
end
# Usage
factory = HeroFactory.instance
another_factory = HeroFactory.instance
puts factory == another_factory
# => true
HeroFactory.new
# => Raise Exception- This pattern tries to simplify complicated control flows changing an object's behavior dynamically.[link]
class Operation
attr_reader :state
def initialize
@state = OperationOpenState.new
end
def trigger(state)
@state = @state.next(state)
end
end
class OperationOpenState
def next(state)
if valid?(state)
OperationPendingPaymentState.new
else
raise IllegalStateJumpError
end
end
def valid?(state)
state == :pending_payment
end
end
class OperationPendingPaymentState
def next(state)
OperationConfirmState.new if valid?(state)
end
def valid?(state)
state == :confirm
end
end
class IllegalStateJumpError < StandardError; end
class OperationConfirmState; end
#Usage
operation = Operation.new
puts operation.state.class
#=> OperationOpenState
operation.trigger :pending_payment
puts operation.state.class
#=> OperationPendingPaymentState
operation.trigger :confirm
puts operation.state.class
#=> OperationConfirmState
operation = Operation.new
operation.trigger :confirm
#=> raise IllegalStateJumpError- Define a family of algorithms, encapsulate each one, and make them interchangeable.[link]
class Hero
attr_reader :damage, :health, :skills
attr_accessor :printer
def initialize(printer)
@damage = 10
@health = 5
@printer = printer
@skills = [:stealth, :driving, :intimidation]
end
def print_stats
if block_given?
yield(damage, health, skills)
else
printer.print(damage, health, skills)
end
end
end
class BattleStats
def print(damage, health, skills)
"Damage: #{damage}\nHealth: #{health}"
end
end
class SkillStats
def print(damage, health, skills)
skills.inject(""){ |result, skill| result + skill.to_s.capitalize + "\n" }
end
end
# Usage
Hero.new(BattleStats.new).print_stats
# => Damage: 10
# Health: 5
Hero.new(SkillStats.new).print_stats
# => Stealth
# Driving
# Intimidation
Hero.new(any_printer).print_stats do |damage, health, skills|
"Looks: I'm printing a customize message about my hero with damage #{damage} and number of skills: #{skills.size}"
end- Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template methods lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.[link]
class Hero
attr_reader :damage, :abilities
def initialize
@damage = damage_rating
@abilities = occupation_abilities
end
def greet
greeting = ["Hello"]
greeting << unique_greeting_line
greeting
end
def unique_greeting_line
raise "You must define unique_greeting_line"
end
def damage_rating
10
end
def occupation_abilities
[]
end
def attack
"Atack dealing #{damage} damage"
end
end
class Warrior < Hero
def damage_rating
15
end
def occupation_abilities
[:strike]
end
def unique_greeting_line
"Warrior is ready to fight!"
end
end
class Mage < Hero
def damage_rating
7
end
def occupation_abilities
[:magic_spell]
end
def unique_greeting_line
"Mage is ready to make powerful spells!"
end
end