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ModernPHP
NewFeaturesandGoodPractices
JoshLockhart

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ModernPHP
byJoshLockhart
Copyright©2015JoshLockhart.Allrightsreserved.
PrintedintheUnitedStatesofAmerica.
PublishedbyO’ReillyMedia,Inc.,1005GravensteinHighwayNorth,Sebastopol,CA
95472.
O’Reillybooksmaybepurchasedforeducational,business,orsalespromotionaluse.
Onlineeditionsarealsoavailableformosttitles().Formore
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Editor:AllysonMacDonald
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InteriorDesigner:DavidFutato
CoverDesigner:EllieVolckhausen
Illustrator:RebeccaDemarest
February2015:FirstEdition

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RevisionHistoryfortheFirstEdition
2015-02-09:FirstRelease
Seeforreleasedetails.
TheO’ReillylogoisaregisteredtrademarkofO’ReillyMedia,Inc.ModernPHP,the
coverimage,andrelatedtradedressaretrademarksofO’ReillyMedia,Inc.
Whilethepublisherandtheauthorhaveusedgoodfaitheffortstoensurethatthe
informationandinstructionscontainedinthisworkareaccurate,thepublisherandthe
authordisclaimallresponsibilityforerrorsoromissions,includingwithoutlimitation
responsibilityfordamagesresultingfromtheuseoforrelianceonthiswork.Useofthe
informationandinstructionscontainedinthisworkisatyourownrisk.Ifanycode
samplesorothertechnologythisworkcontainsordescribesissubjecttoopensource
licensesortheintellectualpropertyrightsofothers,itisyourresponsibilitytoensurethat
yourusethereofcomplieswithsuchlicensesand/orrights.
978-1-491-90501-2
[LSI]

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ForLaurel

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Preface
ThereareamillionPHPtutorialsonline.Mostofthesetutorialsareoutdatedand
demonstrateobsoletepractices.Unfortunately,thesetutorialsarestillreferencedtoday

thankstotheirGoogleimmortality.OutdatedinformationisdangeroustounawarePHP
programmerswhounknowinglycreateslowandinsecurePHPapplications.Irecognized
thisissuein2013,anditistheprimaryreasonIbeganPHPTheRightWay,acommunity
initiativetoprovidePHPprogrammerseasyaccesstohigh-qualityandup-to-date
informationfromauthoritativemembersofthePHPcommunity.
ModernPHPismynextendeavortowardthesamegoal.Thisbookisnotareference
manual.Nope.Thisbookisafriendlyandfunconversationbetweenyouandme.I’ll
introduceyoutothemodernPHPprogramminglanguage.I’llshowyouthelatestPHP
techniquesthatIuseeverydayatworkandonmyopensourceprojects.AndI’llhelpyou
usethelatestcodingstandardssoyoucanshareyourPHPcomponentsandlibrarieswith
thePHPcommunity.
You’llhearmesay“community”overandover(andover).ThePHPcommunityis
friendlyandhelpfulandwelcoming—althoughnotwithoutoccasionaldrama.Ifyou
becomecuriousaboutaspecificfeaturementionedinthisbook,reachouttoyourlocal
PHPusergroupwithquestions.IguaranteeyoutherearenearbyPHPdeveloperswho
wouldlovetohelpyoubecomeabetterPHPprogrammer.YourlocalPHPusergroupisan
invaluableresourceasyoucontinuetoimproveyourPHPskillslongafteryoufinishthis
book.

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WhatYouNeedtoKnowAboutThisBook
Beforewegetstarted,Iwanttosetafewexpectations.First,itisimpossibleformeto
covereverywaytousePHP.Thereisn’tenoughtime.Instead,IwillshowyouhowIuse
PHP.Yes,thisisanopinionatedapproach,butIusetheverysamepracticesandstandards
adoptedbymanyotherPHPdevelopers.Whatyoutakeawayfromourbriefconversation
willbeimmediatelyapplicableinyourownprojects.
Second,Iassumeyouarefamiliarwithvariables,conditionals,loops,andsoon;youdon’t
havetoknowPHP,butyoushouldatleastbringabasicunderstandingofthese

fundamentalprogrammingconcepts.Youcanalsobringcoffee(Ilovecoffee).I’llsupply
everythingelse.
Third,Idonotassumeyouareusingaspecificoperatingsystem.However,mycode
examplesarewrittenforLinux.BashcommandsareprovidedforUbuntuandCentOSand
mayalsoworkonOSX.IfyouuseWindows,IhighlyrecommendyouspinupaLinux
virtualmachinesoyoucanruntheexamplecodeinthisbook.

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HowThisBookIsOrganized
PartIdemonstratesnewPHPfeatureslikenamespaces,generators,andtraits.Itintroduces
youtothemodernPHPlanguage,anditexposesyoutofeaturesyoumaynothaveknown
aboutuntilnow.
PartIIexploresgoodpracticesthatyoushouldimplementinyourPHPapplications.Have
youheardthetermPSR,butyou’renotentirelysurewhatitisorhowtouseit?Doyou
wanttolearnhowtosanitizeuserinputandusesafedatabasequeries?Thischapterisfor
you.
PartIIIismoretechnicalthanthefirsttwoparts.Itdemonstrateshowtodeploy,tune,test,
andprofilePHPapplications.WediveintodeploymentstrategieswithCapistrano.Wetalk
abouttestingtoolslikePHPUnitandTravisCI.AndweexplorehowtotunePHPsoit
performsaswellaspossibleforyourapplication.
AppendixAprovidesstep-by-stepinstructionsforinstallingandconfiguringPHP-FPMon
yourmachine.
AppendixBexplainshowtobuildalocaldevelopmentenvironmentthatcloselymatches
yourproductionserver.WeexploreVagrant,Puppet,Chef,andalternativetoolstohelp
yougetstartedquickly.

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ConventionsUsedinThisBook
Thefollowingtypographicalconventionsareusedinthisbook:
Italic
Indicatesnewterms,URLs,emailaddresses,filenames,andfileextensions.
Constantwidth

Usedforprogramlistings,aswellaswithinparagraphstorefertoprogramelements
suchasvariableorfunctionnames,databases,datatypes,environmentvariables,
statements,andkeywords.
Constantwidthbold

Showscommandsorothertextthatshouldbetypedliterallybytheuser.
Constantwidthitalic

Showstextthatshouldbereplacedwithuser-suppliedvaluesorbyvaluesdetermined
bycontext.
Tip
Thiselementsignifiesatiporsuggestion.
Note
Thiselementsignifiesageneralnote.
Warning
Thiselementindicatesawarningorcaution.

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UsingCodeExamples
Supplementalmaterial(codeexamples,exercises,etc.)isavailablefordownloadat
/>Thisbookisheretohelpyougetyourjobdone.Ingeneral,ifexamplecodeisoffered

withthisbook,youmayuseitinyourprogramsanddocumentation.Youdonotneedto
contactusforpermissionunlessyou’rereproducingasignificantportionofthecode.For
example,writingaprogramthatusesseveralchunksofcodefromthisbookdoesnot
requirepermission.SellingordistributingaCD-ROMofexamplesfromO’Reillybooks
doesrequirepermission.Answeringaquestionbycitingthisbookandquotingexample
codedoesnotrequirepermission.Incorporatingasignificantamountofexamplecode
fromthisbookintoyourproduct’sdocumentationdoesrequirepermission.
Weappreciate,butdonotrequire,attribution.Anattributionusuallyincludesthetitle,
author,publisher,andISBN.Forexample:“ModernPHPbyJoshLockhart(O’Reilly).
Copyright2015JoshLockhart,978-1-491-90501-2.”
Ifyoufeelyouruseofcodeexamplesfallsoutsidefairuseorthepermissiongivenabove,
feelfreetocontactusat

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Acknowledgments
Thisismyfirstbook.WhenO’ReillyapproachedmeaboutwritingModernPHP,Iwas
equallyexcitedandscaredtodeath.ThefirstthingIdidwasaWalterHustondance;I
mean,O’Reillywantedmetowriteabook.Howcoolisthat!?ThenIaskedmyselfcanI
reallywritethatmanypages?Abookisn’taquickorsmalltask.
Ofcourse,Iimmediatelysaid“yes.”IknewIcouldwriteModernPHPbecauseIhad
family,friends,coworkers,editors,andreviewerssupportingmetheentireway.Iwantto

acknowledgeandthankmysupportersfortheirinvaluablefeedback.Withoutthem,this
bookwouldneverhavehappened.
First,IwanttothankmyeditoratO’ReillyMedia—AllysonMacDonald
(@allyatoreilly).Allywasnice,critical,supportive,andsmart.Sheknewexactlyhowand
whentogentlynudgemeintherightdirectionwheneverIgotofftrack.Ican’timagine
workingwithabettereditor.
Ialsowanttothankmytechnicalreviewers—AdamFairholm(@adamfairholm)andEd
Finkler(@funkatron).AdamisabrilliantwebdeveloperatNewfangled,andheisperhaps
bestknownforhisworkonIMVDb—thepopularmusicvideodatabase.EdiswellknownthroughoutthePHPcommunityforhisincrediblePHPskills,hispersonalityonthe
/dev/hellpodcast,andhiscommendableOpenSourcingMentalIllnesscampaign.Adam
andEdbothpointedouteverythingdumb,illogical,andincorrectinmyearlydrafts.This
bookisfarbetterthananythingIcouldwriteonmyownthankstotheirbrutallyhonest
feedback.Iamforeverindebtedtothemfortheirguidanceandwisdom.Ifanyfaultsor
inaccuracieswriggledtheirwayintothefinalmanuscript,thosefaultsaresurelymyown.
MycoworkersatNewMediaCampaignshavebeenaconstantsourceofencouragement.
Joel,Clay,Kris,Alex,Patrick,Ashley,Lenny,Claire,Todd,Pascale,Henry,andNathan
—Itipmyhattoallofyouforyourkindwordsofencouragementfrombeginningtoend.
Andmostimportant,Iwanttothankmyfamily—Laurel,Ethan,Tessa,Charlie,Lisa,
Glenn,andLiz.Thankyouforyourencouragement,withoutwhichIwouldhavenever
finishedthisbook.Tomylovelywife,Laurel,thankyouforyourpatience.Thankyoufor
accompanyingmetoCaribouCoffeeforsomanylate-nightwritingsessions.Thankyou
forlettingmeabandonyouonweekends.Thankyouforkeepingmemotivatedandon
schedule.Iloveyounowandforever.

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PartI.LanguageFeatures

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Chapter1.TheNewPHP
ThePHPlanguageisexperiencingarenaissance.PHPistransformingintoamodern
scriptinglanguagewithhelpfulfeatureslikenamespaces,traits,closures,andabuilt-in
opcodecache.ThemodernPHPecosystemisevolving,too.PHPdevelopersrelylesson
monolithicframeworksandmoreonsmallerspecializedcomponents.TheComposer
dependencymanagerisrevolutionizinghowwebuildPHPapplications;itemancipatesus
fromaframework’swalledgardenandletsusmixandmatchinteroperablePHP
componentsbestsuitedforourcustomPHPapplications.Componentinteroperability
wouldnotbepossiblewithoutcommunitystandardsproposedandcuratedbythePHP
FrameworkInteropGroup.
ModernPHPisyourguidetothenewPHP,anditwillshowyouhowtobuildanddeploy
amazingPHPapplicationsusingcommunitystandards,goodpractices,andinteroperable
components.

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Past
BeforeweexploremodernPHP,itisimportanttounderstandPHP’sorigin.PHPisan
interpretedserver-sidescriptinglanguage.ThismeansyouwritePHPcode,uploadittoa
webserver,andexecuteitwithaninterpreter.PHPistypicallyusedwithawebserverlike
Apacheornginxtoservedynamiccontent.However,PHPcanalsobeusedtobuild
powerfulcommand-lineapplications(justlikebash,Ruby,Python,andsoon).ManyPHP
developersdon’trealizethisandmissoutonareallyexcitingfeature.Notyou,though.
YoucanreadtheofficialPHPhistoryatIwon’t
repeatwhathasalreadybeensaidsowellbyRasmusLerdorf(thecreatorofPHP).WhatI
willtellyouisthatPHPhasatumultuouspast.PHPbeganasacollectionofCGIscripts
writtenbyRasmusLerdorftotrackvisitstohisonlineresume.Lerdorfnamedhissetof

CGIscripts“PersonalHomePageTools.”Thisearlyincarnationwascompletelydifferent
fromthePHPweknowtoday.Lerdorf’searlyPHPToolswerenotascriptinglanguage;
theyweretoolsthatprovidedrudimentaryvariablesandautomaticformvariable
interpretationusinganHTMLembeddedsyntax.
Between1994and1998,PHPunderwentnumerousrevisionsandevenreceivedafew
ground-uprewrites.AndiGutmansandZeevSuraski,twodevelopersfromTelAviv,
joinedforceswithRasmusLerdorftotransformPHPfromasmallcollectionofCGItools
intoafull-fledgedprogramminglanguagewithamoreconsistentsyntaxandbasicsupport
forobject-orientedprogramming.TheynamedtheirfinalproductPHP3andreleaseditin
late1998.ThenewPHPmonikerwasadeparturefromearliernames,anditisarecursive
acronymforPHP:HypertextPreprocessor.PHP3wasthefirstversionthatmost
resembledthePHPweknowtoday.Itprovidedsuperiorextensibilitytovariousdatabases,
protocols,andAPIs.PHP3’sextensibilityattractedmanynewdeveloperstotheproject.
Bylate1998,PHP3wasalreadyinstalledonastaggering10%oftheworld’swebservers.

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Present
Today,thePHPlanguageisquicklyevolvingandissupportedbydozensofcoreteam
developersfromaroundtheworld.Developmentpracticeshavechanged,too.Inthepast,
itwascommonpracticetowriteaPHPfile,uploadittoaproductionserverwithFTP,and
hopeitworked.Thisisaterribledevelopmentstrategy,butitwasnecessaryduetoalack
ofviablelocaldevelopmentenvironments.
Nowadays,weeschewFTPanduseversioncontrolinstead.Versioncontrolsoftwarelike
Githelpsmaintainanauditablecodehistorythatcanbebranched,forked,andmerged.
Localdevelopmentenvironmentsareidenticaltoproductionserversthanksto
virtualizationtoolslikeVagrantandprovisioningtoolslikeAnsible,Chef,andPuppet.We
leveragespecializedPHPcomponentswiththeComposerdependencymanager.OurPHP
codeadherestoPSRs—communitystandardsmanagedbythePHPFrameworkInterop

Group.WethoroughlytestourcodewithtoolslikePHPUnit.Wedeployourapplications
withPHP’sFastCGIprocessmanagerbehindawebserverlikenginx.Andweincrease
applicationperformancewithanopcodecache.
ModernPHPencompassesmanynewpracticesthatmaybeunfamiliartothoseofyounew
toPHP,ortothoseupgradingfromolderPHPversions.Don’tfeeloverwhelmed.I’llwalk
througheachconceptlaterinthisbook.
I’malsoexcitedthatPHPnowhasanofficialdraftspecification—somethingitlacked
until2014.
Note
Mostmatureprogramminglanguageshaveaspecification.Inlayman’sterms,a
specificationisacanonicalblueprintthatdefineswhatitmeanstobePHP.Thisblueprint
isusedbydeveloperswhocreateprogramsthatparse,interpret,andexecutePHPcode.It
isnotfordeveloperswhocreateapplicationsandwebsiteswithPHP.
SaraGolemonandFacebookannouncedthefirstPHPspecificationdraftatO’Reilly’s
OSCONconferencein2014.YoucanreadtheofficialannouncementonthePHPinternals
mailinglist,andyoucanreadthePHPspecificationonGitHub.
AnofficialPHPlanguagespecificationisbecomingmoreimportantgiventheintroduction
ofmultiplecompetingPHPengines.TheoriginalPHPengineistheZendEngine,aPHP
interpreterwritteninCandintroducedinPHP4.TheZendEnginewascreatedbyRasmus
Lerdorf,AndiGutmans,andZeevSuraski.TodaytheZendEngineistheZendcompany’s
maincontributiontothePHPcommunity.However,thereisnowasecondmajorPHP
engine—theHipHopVirtualMachinefromFacebook.Alanguagespecificationensures
thatbothenginesmaintainabaselinecompatibility.
Note
APHPengineisaprogramthatparses,interprets,andexecutesPHPcode(e.g.,theZend
EngineorFacebook’sHipHopVirtualMachine).ThisisnottobeconfusedwithPHP,
whichisagenericreferencetothePHPlanguage.

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Future
TheZendEngineisimprovingatarapidpacewithnewfeaturesandimproved
performance.IattributetheZendEngine’simprovementstoitsnewcompetition,
specificallyFacebook’sHipHopVirtualMachineandHackprogramminglanguage.
HackisanewprogramminglanguagebuiltontopofPHP.Itintroducesstatictyping,new
datastructures,andadditionalinterfaceswhilemaintainingbackwardcompatibilitywith
existingdynamicallytypedPHPcode.Hackistargetedatdeveloperswhoappreciate
PHP’srapiddevelopmentcharacteristicsbutneedthepredictabilityandstabilityfrom
statictyping.
Note
We’lldiscussdynamicversusstatictypinglaterinthisbook.Thedifferencebetweenthe
twoiswhenPHPtypesarechecked.Dynamictypesarecheckedatruntime,whereasstatic
typesarecheckedatcompiletime.JumpaheadtoChapter12formoreinformation.
TheHipHopVirtualMachine(HHVM)isaPHPandHackinterpreterthatusesajustin
time(JIT)compilertoimproveapplicationperformanceandreducememoryusage.
Idon’tforeseeHackandHHVMreplacingtheZendEngine,butFacebook’snew
contributionsarecreatingagiantsplashinthePHPcommunity.Increasingcompetition
haspromptedtheZendEnginecoreteamtoannouncePHP7,anoptimizedZendEngine
saidtobeonparwithHHVM.We’lldiscussthesedevelopmentsfurtherinChapter12.
It’sanexcitingtimetobeaPHPprogrammer.ThePHPcommunityhasneverbeenthis
energized,fun,andinnovative.IhopethisbookhelpsyoufirmlyembracemodernPHP
practices.Thereareatonofnewthingstolearn,andmanymorethingsonthehorizon.
Considerthisyourroadmap.Nowlet’sgetstarted.

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Chapter2.Features
ThemodernPHPlanguagehasmanyexcitingnewfeatures.Manyofthesefeatureswillbe

brandnewtoPHPprogrammersupgradingfromearlierversions,andthey’llbeanice
surprisetoprogrammersmigratingtoPHPfromanotherlanguage.Thesenewfeatures
makethePHPlanguageapowerfulplatformandprovideapleasantexperiencefor
buildingwebapplicationsandcommand-linetools.
Someofthesefeaturesaren’tessential,buttheystillmakeourliveseasier.Somefeatures,
however,areessential.Namespaces,forexample,areacornerstoneofmodernPHP
standardsandenabledevelopmentpracticesthatmodernPHPdeveloperstakeforgranted
(e.g.,autoloading).I’llintroduceeachnewfeature,explainwhyitisuseful,andshowyou
howtoimplementitinyourownprojects.
Tip
Iencourageyoutofollowalongonyourowncomputer.Youcanfindallofthetext’scode
examplesinthisbook’scompanionGitHubrepository.

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Namespaces
IfthereisonemodernPHPfeatureIwantyoutoknow,itisnamespaces.Introducedin
PHP5.3.0,namespacesareanimportanttoolthatorganizesPHPcodeintoavirtual
hierarchy,comparabletoyouroperatingsystem’sfilesystemdirectorystructure.Each
modernPHPcomponentandframeworkorganizesitscodebeneathitsownglobally
uniquevendornamespacesothatitdoesnotconflictwith,orlayclaimto,commonclass
namesusedbyothervendors.
Note
Don’tyouhateitwhenyouwalkintoacoffeeshopandthisoneobnoxiouspersonhasa
messofbooks,cables,andwhatnotspreadacrossseveraltables?Nottomentionhe’s
sittingnextto,butnotusing,theonlyavailablepoweroutlet.He’swastingvaluablespace
thatcouldotherwisebeusefultoyou.Figurativelyspeaking,thispersonisnotusing
namespaces.Don’tbethisperson.
Let’sseehowareal-worldPHPcomponentusesnamespaces.TheSymfonyFramework’s

ownsymfony/httpfoundationisapopularPHPcomponentthatmanagesHTTPrequests
andresponses.Moreimportant,thesymfony/httpfoundationcomponentusescommon
PHPclassnameslikeRequest,Response,andCookie.Iguaranteeyoutherearemany
otherPHPcomponentsthatusethesesameclassnames.Howcanweusethe
symfony/httpfoundationPHPcomponentifotherPHPcodeusesthesameclassnames?
Wecansafelyusethesymfony/httpfoundationcomponentpreciselybecauseitscodeis
sandboxedbeneaththeuniqueSymfonyvendornamespace.Visitthe
symfony/httpfoundationcomponentonGitHubandnavigatetotheResponse.phpfile.It
lookslikeFigure2-1.

Figure2-1.GitHubsymfony/httpfoundationscreenshot
Lookcloselyatline12.Itcontainsthiscode:
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namespaceSymfony\Component\HttpFoundation;

ThisisaPHPnamespacedeclaration,anditalwaysappearsonanewlineimmediately
aftertheopeningFirst,weknowtheResponseclasslivesbeneaththeSymfonyvendornamespace(the
vendornamespaceisthetopmostnamespace).WeknowtheResponseclasslivesbeneath
theComponentsubnamespace.WealsoknowtheResponseclasslivesbeneathyetanother
subnamespacenamedHttpFoundation.Youcanviewotherfilesadjacentto
Response.php,andyou’llseetheyusethesamenamespacedeclaration.Anamespace(or
subnamespace)encapsulatesandorganizesrelatedPHPclasses,justasafilesystem
directorycontainsrelatedfiles.
Tip
Subnamespacesareseparatedwitha\character.
Unlikeyouroperatingsystem’sphysicalfilesystem,PHPnamespacesareavirtualconcept
anddonotnecessarilymap1:1withfilesystemdirectories.Thatbeingsaid,mostPHP

componentsdo,infact,mapsubnamespacestofilesystemdirectoriesforcompatibility
withthepopularPSR-4autoloaderstandard(we’lltalkmoreaboutthisinChapter3).
Note
Technicallyspeaking,namespacesaremerelyaPHPlanguagenotationreferencedbythe
PHPinterpretertoapplyacommonnameprefixtoasetofclasses,interfaces,functions,
andconstants.

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WhyWeUseNamespaces
Namespacesareimportantbecausetheyletuscreatesandboxedcodethatworksalongside
otherdevelopers’code.ThisisthecornerstoneconceptofthemodernPHPcomponent
ecosystem.Componentandframeworkauthorsbuildanddistributecodeforalarge
numberofPHPdevelopers,andtheyhavenowayofknowingorcontrollingwhatclasses,
interfaces,functions,andconstantsareusedalongsidetheirowncode.Thisproblem
appliestoyourownin-houseprojects,too.IfyouwritecustomPHPcomponentsor
classesforaproject,thatcodemustworkalongsideyourproject’sthird-party
dependencies.
AsImentionedearlierwiththesymfony/httpfoundationcomponent,yourcodeand
otherdevelopers’codemightusethesameclass,interface,function,orconstantnames.
Withoutnamespaces,anamecollisioncausesPHPtofail.Withnamespaces,yourcode
andotherdevelopers’codecanusethesameclass,interface,function,orconstantname
assumingyourcodelivesbeneathauniquevendornamespace.
Ifyou’rebuildingatinypersonalprojectwithonlyafewdependencies,classname
collisionsprobablywon’tbeanissue.Butwhenyou’reworkingonateambuildingalarge
projectwithnumerousthird-partydependencies,namecollisionsbecomeaveryreal
concern.Youcannotcontrolwhichclasses,interfaces,functions,andconstantsare
introducedintotheglobalnamespacebyyourproject’sdependencies.Thisiswhy
namespacingyourcodeisimportant.


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Declaration
EveryPHPclass,interface,function,andconstantlivesbeneathanamespace(or
subnamespace).NamespacesaredeclaredatthetopofaPHPfileonanewline
immediatelyaftertheopeningnamespace,thenaspacecharacter,thenthenamespacename,andthenaclosing
semicolon;character.
Rememberthatnamespacesareoftenusedtoestablishatop-levelvendorname.This
examplenamespacedeclarationestablishestheOreillyvendorname:
namespaceOreilly;

AllPHPclasses,interfaces,functions,orconstantsdeclaredbeneaththisnamespace
declarationliveintheOreillynamespaceandare,insomeway,relatedtoO’Reilly
Media.Whatifwewantedtoorganizecoderelatedtothisbook?Weuseasubnamespace.
Subnamespacesaredeclaredexactlythesameasinthepreviousexample.Theonly
differenceisthatweseparatenamespaceandsubnamespacenameswiththe\character.
ThefollowingexampledeclaresasubnamespacenamedModernPHPthatlivesbeneaththe
topmostOreillyvendornamespace:
namespaceOreilly\ModernPHP;

Allclasses,interfaces,functions,andconstantsdeclaredbeneaththisnamespace
declarationliveintheOreilly\ModernPHPsubnamespaceandare,insomeway,relatedto
thisbook.
Allclassesinthesamenamespaceorsubnamespacedon’thavetobedeclaredinthesame
PHPfile.YoucanspecifyanamespaceorsubnamespaceatthetopofanyPHPfile,and

thatfile’scodebecomesapartofthatnamespaceorsubnamespace.Thismakesitpossible
towritemultipleclassesinseparatefilesthatbelongtoacommonnamespace.
Tip
Themostimportantnamespaceisthevendornamespace.Thisisthetopmostnamespace
thatidentifiesyourbrandororganization,anditmustbegloballyunique.Subnamespaces
arelessimportant,buttheyarehelpfulfororganizingyourproject’scode.

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ImportandAlias
Beforewehadnamespaces,PHPdeveloperssolvedthenamecollisionproblemwith
Zend-styleclassnames.Thiswasaclass-namingschemepopularizedbytheZend
FrameworkwherePHPclassnamesusedunderscoresinlieuoffilesystemdirectory
separators.Thisconventionaccomplishedtwothings:itensuredclassnameswereunique,
anditenabledanaiveautoloaderimplementationthatreplacedunderscoresinPHPclass
nameswithfilesystemdirectoryseparatorstodeterminetheclassfilepath.
Forexample,thePHPclass
Zend_Cloud_DocumentService_Adapter_WindowsAzure_QuerycorrespondstothePHP

fileZend/Cloud/DocumentService/Adapter/WindowsAzure/Query.php.Asideeffectofthe
Zend-stylenamingconvention,asyoucansee,isabsurdlylongclassnames.Callmelazy,
butthere’snowayI’mtypingthatclassnamemorethanonce.
ModernPHPnamespacespresentasimilarproblem.Forexample,thefullResponseclass
nameinthesymfony\httpfoundationcomponentis
\Symfony\Component\HttpFoundation\Response.Fortunately,PHPletsusimportand
aliasnamespacedcode.
Byimport,ImeanthatItellPHPwhichnamespaces,classes,interfaces,functions,and
constantsIwilluseineachPHPfile.Icanthenusethesewithouttypingtheirfull
namespaces.

Byalias,ImeanthatItellPHPthatIwillreferenceanimportedclass,interface,function,
orconstantwithashortername.
Tip
YoucanimportandaliasPHPclasses,interfaces,andothernamespacesasofPHP5.3.
YoucanimportandaliasPHPfunctionsandconstantsasofPHP5.6.
ThecodeshowninExample2-1createsandsendsa400BadRequestHTTPresponse
withoutimportingandaliasing.
Example2-1.Namespacewithoutalias
$response=new\Symfony\Component\HttpFoundation\Response('Oops',400);
$response->send();

Thisisn’tterrible,butimagineyouhavetoinstantiateaResponseinstanceseveraltimesin
asinglePHPfile.Yourfingerswillgettiredquickly.NowlookatExample2-2.Itdoesthe
samethingwithimporting.
Example2-2.Namespacewithdefaultalias
useSymfony\Component\HttpFoundation\Response;
$response=newResponse('Oops',400);
$response->send();

WetellPHPweintendtousetheSymfony\Component\HttpFoundation\Responseclass
withtheusekeyword.Wetypethelong,fullyqualifiedclassnameonce.Thenwecan
instantiatetheResponseclasswithoutusingitsfullynamespacedclassname.Howcoolis
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that?
SomedaysIfeelreallylazy.Thisisagoodopportunitytouseanalias.Let’sextend
Example2-2.InsteadoftypingResponse,maybeIjustwanttotypeResinstead.

Example2-3showshowIcandothat.
Example2-3.Namespacewithcustomalias
useSymfony\Component\HttpFoundation\ResponseasRes;
$r=newRes('Oops',400);
$r->send();

Inthisexample,IchangedtheimportlinetoimporttheResponseclass.Ialsoappended
asRestotheendoftheimportline;thistellsPHPtoconsiderResanaliasforthe
Responseclass.Ifwedon’tappendtheasResaliastotheimportline,PHPassumesa
defaultaliasthatisthesameastheimportedclassname.
Tip
YoushouldimportcodewiththeusekeywordatthetopofeachPHPfile,immediately
aftertheopeningYoudon’tneedaleading\characterwhenimportingcodewiththeusekeywordbecause
PHPassumesimportednamespacesarefullyqualified.
Theusekeywordmustexistintheglobalscope(i.e.,notinsideofaclassorfunction)
becauseitisusedatcompiletime.Itcan,however,belocatedbeneathanamespace
declarationtoimportcodeintoanothernamespace.
AsofPHP5.6,it’spossibletoimportfunctionsandconstants.Thisrequiresatweaktothe
usekeywordsyntax.Toimportafunction,changeusetousefunc:
usefuncNamespace\functionName;
functionName();

Toimportaconstant,changeusetouseconstant:
useconstantNamespace\CONST_NAME;
echoCONST_NAME;


Functionandconstantaliasesworkthesameasclasses.

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