1. Introduction2. Adapter3. Builder4. Command5. Composite6. Decorator7. Factory8. Iterator9. Observer

10. Proxy11. Singleton12. State13. Strategy14. Template

TableofContents

RubyPatterns

2

ExamplesofPatternsinRuby

1. Adapter2. Builder3. Command4. Composite5. Decorator6. Factory7. Iterator8. Observer9. Proxy

10. Singleton11. State12. Strategy13. Template

RubyPatterns

TableofContents

RubyPatterns

3Introduction

Converttheinterfaceofaclassintoanotherinterfaceclientsexpect.Adapterletsclassesworktogetherthatcouldn'totherwisebecauseofincompatibleinterfaces.

classQuestattr_accessor:difficulty,:hero

definitialize(difficulty)@difficulty=difficulty@hero=nilend

deffinish@hero.exp+=calculate_experienceend

defcalculate_experience@difficulty*50/@hero.levelendend

classHeroattr_accessor:level,:exp,:quests

definitialize@level=1@exp=0@quests=[]end

deftake_quest(quest)@quests

attr_accessor:hero

definitialize(old_quest,difficulty)@old_quest=old_quest@old_quest.difficulty=difficulty@hero=nilend

deffinish@hero.exp+=@old_quest.doneendend

#Usagehero=Hero.newquest=Quest.new5hero.take_questquesthero.finish_questquestputshero.exp#=>250some_old_quest=OldQuest.newold_quest_adapted=QuestAdapter.new(some_old_quest,5)hero.take_questold_quest_adaptedhero.finish_questold_quest_adaptedputshero.exp#=>300

RubyPatterns

5Adapter

Separatetheconstructionofacomplexobjectfromitsrepresentationsothatthesameconstructionprocesscancreatedifferentrepresentations.

classBoardBuilderdefinitialize(width,height)@board=Board.new@board.width=width@board.height=height@board.tiles=[]@board.monsters=[]end

defadd_tiles(n)n.times{@board.tiles2builder.add_tiles(3)builder.add_monsters(2)putsboard.tiles.size#=>3putsboard.monsters.size#=>2

Builder

RubyPatterns

6Builder

Encapsulatearequestasanobject,therebylettingyouparameterizeclientswithdifferentrequests,queueorlogrequests,andsupportundoableoperations.

classTurndefinitialize@commands=[]enddefrun_command(command)command.execute@commands

#Usagehero=Hero.newget_money=GetMoneyCommand.newheroheal=HealCommand.newheroturn=Turn.newturn.run_command(heal)putshero.health#=>110turn.run_command(get_money)putshero.money#=>10turn.undo_commandputshero.money#=>0

RubyPatterns

8Command

Compositionoverinheritance.Composeobjectsintotreestructurestorepresentpart-wholehierarchies.

classCompositeQuestdefinitialize@tasks=[]end

def

RubyPatterns

10Composite

Attachadditionalresponsibilitiestoanobjectdynamically.Decoratorsprovideaflexiblealternativetosubclassingforextendingfunctionality.

classItemDecoratordefinitialize(item)@item=itemend#thisneedstobedelegatedwithotherefectivewaydefuse@item.useendend

classMagicItemDecoratorItemMagic

Decorator

RubyPatterns

11Decorator

masterpiece_item=MasterpieceItemDecorator(item)putsmasterpiece_item.price#=>20putsmasterpiece_item.description#=>ItemMasterpiece

#allnextlinesputs"dosomething"item.usemagic_item.usemasterpiece_item.use

RubyPatterns

12Decorator

Defineaninterfaceforcreatinganobject,butletsubclassesdecidewhichclasstoinstantiate.

classPartyattr_reader:membersdefinitialize(factory)@members=[]@factory=factoryend

defadd_warriors(n)n.times{@members2

Factory

RubyPatterns

13Factory

Iteratorhelpsyoutoiteratethroughacomplexobjectusinganinteratormethod.

classParentattr_reader:first_name

definitialize(first_name,gender)@first_name=first_name@gender=genderendend

classChild6putshero.cursed?#=>true

RubyPatterns

16Observer

Provideasurrogateorplaceholderforanotherobjecttocontrolaccesstoit.

classHeroattr_accessor:keywords

definitialize@keywords=[]endend

classComputerProxy#Forwardableallowsobjectstorunmethodsonbehalf#ofit'smembers,inthiscasetheComputerobjectextendForwardable

#WedelegatetheComputerProxy'suseof#theComputerobject'saddmethoddef_delegators:real_object,:add

definitialize(hero)@hero=heroend

defexecutecheck_accessreal_object.executeend

defcheck_accessunless@hero.keywords.include?(:computer)raise"Youhavenoaccess"endend

defreal_object@real_object||=Computer.newendend

classComputerdefinitialize@queue=[]end

defadd(command)@queue

hero=Hero.newproxy=ComputerProxy.new(hero)proxy.add("somecommand")proxy.execute#=>raiseerrorhero.keywordsexecutingcommands

RubyPatterns

18Proxy

Defineauniqueinstanceofanobject.

classHeroFactory@@instance=nil

defself.instance@@instance||=HeroFactory.send(:new)end

defcreate_warriorWarrior.newend

defcreate_mageMage.newend

private_class_method:newend

#Usagefactory=HeroFactory.instanceanother_factory=HeroFactory.instanceputsfactory==another_factory#=>trueHeroFactory.new#=>RaiseException

Singleton

RubyPatterns

19Singleton

Thispatterntriestosimplifycomplicatedcontrolflowschanginganobject'sbehaviordynamically.

classOperationattr_reader:statedefinitialize@state=OperationOpenState.newend

deftrigger(state)@state=@state.next(state)endend

classOperationOpenStatedefnext(state)valid?(state)?OperationPendingPaymentState.new:raiseIllegalStateJumpErrorend

defvalid?(state)state==:pending_paymentendend

classOperationPendingPaymentStatedefnext(state)OperationConfirmState.newifvalid?(state)end

defvalid?(state)state==:confirmendendclassIllegalStateJumpErrorOperationOpenStateoperation.trigger:pending_paymentputsoperation.state.class#=>OperationPendingPaymentStateoperation.trigger:confirmputsoperation.state.class#=>OperationConfirmState

operation=Operation.newoperation.trigger:confirm#=>raiseIllegalStateJumpError

State

RubyPatterns

20State

Defineafamilyofalgorithms,encapsulateeachone,andmaketheminterchangeable.

classHeroattr_reader:damage,:health,:skillsattr_accessor:printer

definitialize(printer)@damage=10@health=5@printer=printer@skills=[:stealth,:driving,:intimidation]end

defprint_statsifblock_given?yield(damage,health,skills)elseprinter.print(damage,health,skills)endendend

classBattleStatsdefprint(damage,health,skills)"Damage:#{damage}\nHealth:#{health}"endend

classSkillStatsdefprint(damage,health,skills)skills.inject(""){|result,skill|result+skill.to_s.capitalize+"\n"}endend

#UsageHero.new(BattleStats.new)Hero.print_stats#=>Damage:10#Health:5

Hero.new(SkillStats.new)Hero.print_stats#=>Stealth#Driving#Intimidation

Hero.new(any_printer)Hero.print_statsdo|damage,health,skills|"Looks:I'mprintingacustomizemessageaboutmyherowithdamage#{damage}andnumberofskills:end

Strategy

RubyPatterns

21Strategy

Definetheskeletonofanalgorithminanoperation,deferringsomestepstosubclasses.Templatemethodsletssubclassesredefinecertainstepsofanalgorithmwithoutchangingthealgorithm'sstructure.

classHeroattr_reader:damage,:abilities

definitialize@damage=damage_rating@abilities=occupation_abilitiesend

defgreetgreeting=["Hello"]greeting

defoccupation_abilities[:magic_spell]end

defunique_greeting_line"Mageisreadytomakepowerfulspells!"endend

RubyPatterns

23Template

IntroductionAdapterBuilderCommandCompositeDecoratorFactoryIteratorObserverProxySingletonStateStrategyTemplate