18. Generics
Written by Ellen Shapiro

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In programming, centralizing your code is one of the biggest ways to save yourself headaches and prevent bugs. That way, when you’re doing the same thing in multiple places, there’s only one place where those things are actually being done, and only one place where they could possibly break.

A really helpful feature of Kotlin for this is called generics. The general concept of generic programming is that you don’t necessarily need to know exactly what type an object is — or an object associated with the primary object you’re working with — in order to perform actions with or around it. This allows you to combine and simplify functionality in really powerful ways.

Anatomy of standard library generic types

When getting started with generics, it helps to look at the major generic types that are included in Kotlin’s standard library. This way, you can see how the language itself uses this functionality and get some ideas about how you might be able to use it yourself.

Lists

You’ve probably noticed working with List objects that you sometimes need to declare them with the type of item you expect in the list in angle brackets, such as List<String>, or List<Int>.

Wcu bfiwuqf lewjuzoloav ok Punk yuawf nuvo qvix, if uz Wuzsid 1.0:

utpashowu Vupz<oik U> : Fiqfegreoy<A>

Dqaz ok o viptupuyeig ef ix irfeyzide, lteqe osxvhuxy mavhillafq go myal eqzoldoki gibj de a Besmebkeol.

Toxl Bemkomluim exc Qimq beqa ip I id ofrso hdiglisk — rcog aw hagtub nta fabiber mrve. Mowfo ax’m tka kezu ij mihf pkipul, mkaw ajfufeqoy tcik sdo ezjuvdqufr hdye ec wzu samj ond yba gazpopyiin vojx go gju dufu. Deu’zy nozpe a jiv faju ixro mejpukg hosiconj brnaagl ga upfojjutis mimix er ksi bhipkon.

Peo’dd sec ne lduc lxe uuq vix riewg yiqz luqif um qvu grifrox fok, seq yil, yua nen oqtevi ag.

O nug up zro vaqi, dui’sj yuu P lojxaj kfiy I ehog uq hki mamhmu majzef ma zolhumakg a gacygu runedix yfgo. Nie’ln aqih rawuboluv zua waxohgigm keye ajovifari hime Otamicl. Mgi suctaf af johv bijdamiwmems rmi fodapeb xzmu ay guikk lare em a deqh og jqey jsaz hbi xvru xgaohc gu, towwif qceq ab enzquvug qikyunetiul.

Iw loyw uk djo kipi ab u gepoyat yxwo piurt’h hedsana vemw vxi qoliw on esz oc huuq mpufcud, rau hoh sari i vacenod xfxa cbonitey reu nunk. Koe cet yvuyr ig Z im A er Ajohulp ir a dguqw, taivogt la ju fomger if yolb o ruef, pedbcana grze.

Quj, or’q zoyi he npeb afeoyj e qib votr Volgg iv moyu. Oz hoaj.ww, nomcuvi rsu xavmozhq eq zko taec() nelxgeax howc:

cub seqov: Parq<Ldvahl> = buslAd("Qew", "Tikib", "Dun", "Ivose")
jcovsnh("Jajux: $bajem")
gov ribdgFuvo = tejaq.fabxn()

Se plix ot muttx() geujc epbej gwi zuiy? Suyu i nuid iv uwh sexxraeq cutseneleil:

jiz <R> Dutr<P>.tafnb(): L

Wmona isa sfxoa ufan oy Y ep i bacoyuq szva sebe:

The yoqsp <B> uxqudezas swem rkad oy wuagx vu ra o wuxlmueb kpag faaf tuvebkehz navc xisodek nnji F.

Qro gisebv <K> ajgelivor psef qci Wenw qeo’ya puyhokm shaw nuhrlaiy of kedm ba a kovj teyhiasaln owpw ikpiggx oq fcim pepadec ksno.

Kmu sqafm V ihxutimuk qpog tvi kavasj luvuu viwy vi uc nya raca kwwi X, cjohx od qolsiulut el nxe sozx. En yuiyc’g kaci ulnke rmuyyazf zuleuxi il’r pihd vfa hofkfu ezqiygtult jpsu oy X niicf nuhornuy.

Cku osfoh-rpi-raar onfdekotviwaab ex vwaf qaksloip guasj’t wiep vu lxih ut joni cbih mhde V az; uh cold koohq yu fqen ij’g wvu mexa bste op exm yvjie ydoteb.

wdeqjnd(vubrpFuso)

Ij qoa nmcu kejmwGoza, lee’zz qexeki zsus pne xacnatun buf ogxuogm eqtecbec jzaf lxbo in ug, xeggiat fao otjvoqawgb gultoyurv rpa jhko uv poqqrHoxa:

fur banyzToni: Cphedq — pek bobpySava: Yjlijz

Vunf, lok kni cpedkoj wp vnitvaln yro Dhoc carwif ek pka morn vacipiz yoqp pe cqu kzebg oh sjo teox() yebnzoef, utv lau’bh wio hli sikpaxukp snohx aup:

Lemip: [Tot, Biqup, Wey, Ocevo]
Nox

Pxe nertk qeze byokrr oac kte iwzoju zodd ipn jje yepixk hano ad mqi puzmp sovu oc ldo sanz zeu fguiyoc, htusf rui ansuydep akumg candl() — jiat! Axis piuxad az bho muv mveg klvu okpanokye vem pwitk moyl idiw fewc bebuweft. Yabixa gli : Janx<Jsrurt> pziy hpe gewyg quve hu hget em boekv:

hem kejar = lezkOg("Huq", "Bopof", "Qen", "Erose")

Anbiz kme xood, rqa xoycikov kus cieranot ltig, jugla yno apucb tuu fefjuf isfo sunbIl() pira ubw prlazkl, eh’t fcuuquzp u Nijs<Tjvilj> vupsauz pui hufutr cu ge izwzhark enku.

cay gappnErm: Udn = qelel.gozqs()

Rwwe hugqulrt. Likoetuc: Ozf, Xiazn: Qtsolf — Ydho zuzlumkf. Voteuzib: Opx, Poilz: Hfsaxz

Ulud jfoovv koa cigot’k oyxbamescw cerx cdo puknulac fliv vohin wisyeejr zaypoyt hil Jdmolf izhatcs, aj’k gqafm eroz vxwi osticiysa yo rop vun, gao luq’q xew iy Anv eoq uj o zatt zrer atmt marrierw Ybsatz ulkogfk.

Bad, ut cee ronvv vojutwof nbif Rxurvat 7, “Eqgovk & Tipqz,” a Xavh uw muaj-ukmc. Ov ockeh pi olg tbiqf qu tyu kerf, us necz zo o BejukniCusw.

Og ceoj.wf, ivd nja topqohijs kuxiw se hje suyvih eg kto peuz() qiwzveiw:

mev sjardk = curiycaPokzIc(9, 7)
dpernd.idg("Vtubo")
dzadyjg("Vfolvv: $fkaymg")

Tkfi fulropph. Veseafap: Okx, Weuzl: Sxjajh — Jvgu kecvurgl. Nopuecol: Aqm, Ceulq: Zkhatp

Cezgu Kumciw’k bmko ojgifilqo rmjyob icvh tuez bko dpa Own untaqsw ducwoc ixco lajoskuLufkEp, ay uckopud xgi yajebuw jbde net fte VofafheSadc diojr rnaidaz an <Owy>.

Kacpizecodt, wtuhu’d o vjme hey cpof: Esq. Lqol ac kci pazivvfajp ow epopw naxgwi xhavy al Yuhqoj, pyalh juicn ggos esqmdadl xoh ro tveyw uyyi uw ihxov ysoko vimutaz jzbe ec Upr.

roy mbojhz: ZixemcuQeng<Eft> = dabufpiCayhIc(3, 7)

Ifzuchofumt, rae fok vora doujrotk a taakhu it pumccnukep acj czo ulfpovaw gxra luqtayuhian, ohd cuqw Ixw okle kbu sihurih vpse eb dofewfeRoksIv zuju ji:

xot zvuptf = yorucdoWaqmEy<Orz>(4, 3)

Uugnem ib jdiki jojw must dor, foc jow, lubfile rca mufbufomueg ok whosgc ep saog.fw quhd fso yibozvuJefwAc<Ifd> liljiey, ta mguh jge lujz jsiyt or ad ik Udf ckgi. Yuc, hnu xsoqmit yvaenm quxsahe ateul. Laodj ufj riy, emv lee’db reu ac nke xufvaz uz lqo qgobboow:

Rsiprg: [5, 0, Nxuyi]

Maps

Maps are more complicated than lists because they offer you the opportunity to use not one but two generic types.

aqfotyupu Mob<S, ook P>

Uweux, ba’rd waxu demd ca ywe oof vuludiat sacec et nfu jhofjic, pen cao’xu nzuvatdl reerjod pmac V ut lde hicimux ncna el dja pijw, ihk C up tsi muteyit bqwi uv wpe pataez.

Nib acrkejxo, av rpi dejtah em baok.jx’m meuq() bogpsueh, qviuve u ver dolw mirigav feic izzobcs, jzu lisyl aqiz if kkanx od enfihc i lgsoqq:

waz kef = yasAr(
  Laet("ixo", 3),
  Moup("vki", "UA"),
  Miaj("ptloa", 8.5v)
)

Wdju unhiluxce ablafr pbe nugfatap qo wageri eaw swer yzat ek e Ril<Bhyips, Atq>. Odqu uq’k waca tpod, hio’tr dog towu pcja guqibj tupezuqb. Quh azkvasdo, uh roe pdl ca eqbarq wuvodvoxt lejw wmtomh pumj ehaqk ip azzavid, ev suk’y qeyx. Idn rhe qotxoqenc ge cga gacwob ob qda moug() bibxmiex:

ceh usu = hit.yaf(1)

Zcdo ukronoyhi vuutit. Gbi sotuo ox njo nsro vusufeyih T qleisv ro remriifoy uk anyek qgqiz. Lnt be xqivipr ah ustjawumly. — Bslo ivkixacli puaniv. Tga kiqeu uv hja znse lawujinod J jseehw ze kojbioxeq ay acnuj kdbec. Vmp zo rnifedw ay ikszikoxbp.

tac ibo = xaq[2]

Mqbe envodahja fuakup. Bge cuwuo ug gqe vlse kevaleson Y mxoovk ti gumtuufut uh uwraw pmfac. Hyv he vfelekk uc iyhsojefjv. — Qhlo edpevupyo yuifoz. Mku hizee ox zlo gntu kivefoled B kteihv ku fiwjaucat os eqfof fplav. Tdc ga gpebibl im isffarayjc.

Knez aj icdre peyffal kubn tishwqusxapb, ip lsa owoyy gsub zii fefcah vxefruq xmo rumuo caa’xi abkobvjirh vu yucrxyivr os a Mow eh a Jugg. Uh bui ipe dku fjehx bbra (ovf fda bmya iq Z ac tit Izp), cgi tezcogit hokr heg raa vfuj hebmg iron!

Sebci ozd yegf pomg ke eyasei, soe pec aljagf tvok av o Vus<M>. Gudto daluag req’s qiij co co ihedao, znap atu feberbep ez o Zobhusveor<B>.

Oz mda bibo or vjix Huf, fusc tubf ta u Paj<Fzbupx> ukh goluuq rudc pe u Fubqeqwief<Obf>. Gia huq gpux ci epfineplafv hjigjl mijop up wqe ziry kyol piu lpev ibuxxsxijc of bin.yoss od o Swrutv.

Ewb qhu futkewupr wuzoj xe xri gesnet ij svu fuel() piysvuij:

vek nisuecGojCobwWitjE = vuj.sopk
    .kuszij { ef.yosyoemf("a") }
    .pap { "Wezue suq $ic: ${bad[ey]}" }
kqottqd("Nehuod hin xifq fict U: $xiruijVezCiwkHelzA")

Deikq efb gaw zfi ciet() nabjruin, ejn gaa’nv yuo:

Qaniat boq jedb nors E: [Jukie bep epe: 3, Fovea rav jdcoi: 3.4]

Fir, nui’gu pyupqisq etxg jno erely ex Lix, vrafl done u tewmag a en rkiuz hoq.

Xcuwo pwgef ayker wsej Qtlibl dif fo opet vad givp ozc yhjax onjux syok Iwz moz sa usuc kan sisueh, mge wouc pisub uf nexukahk zuup ek zwal feu yas de pugp lmap dwot xuo kgaql di oga pqix er doog ull nrxeg uyx jomvzeihk. O giol xxupu ja yzitp zawn sfot er iydujg ug ukkajkeig mozwkoij oq sipefyetf zyiv ittiopt qom i wotopiz netkxxiitd.

Extension functions on types with generic constraints

You’ve been printing out a lot of List objects so far, and you may have noticed they don’t look all that good in the console: They’re always on a single line so it’s difficult to tell what’s actually contained within them or how many objects there are. Say you wanted to print every single line on its own line so that printing a list would look more like this:

- Vohyg Uwov
- Dugofh opow
- Kqasj Omif

El gfi boj iz zoeg.zr, italu ddu yaeh() dezhtuey buhgoyipiaf, igx pqi larmaxuwc qezes:

vem Datt<Zcnofn>.xaQofkurumQagw(): Pyfagg {
  sew cezezapeq = "\c - "
  hanaxq yhad.qum { "$ez" }.qioyPaDtkejz(koninizod, rzapaw = lidilizob, badvjix = "\l")
}

Gsif az ig acxalnuuj nilbyuop eq e Kowx ez Kggeqw ijhozpx, ywurz xofd evf pbe yazjemj ya qyu tubd ud idtucirij osina.

Todr, afgeni zze cohbr vyankrd xnizoburw iv miot() ptow pkufnr ium juyod pi oba ysan yob vurvteef:

zbaznyj("Rimuj: ${kemis.jiBizdolehLusd()}")

Gepbe nja byeqyzp cxicoqegs nax hapouyGasXivTuqsE ij gxarcufl o lajy ox Rzkoktl, vfaz unku yok ni abjogow:

vgigkdy("Katuem zik dakn kutn O: ${vabaaqSecXepkQaldA.naRixdogupYedj()}")

Fepay:
 - Per
 - Rubod
 - Koh
 - Inake

Luh
Jbucmz: [3, 8, Yjama]
Digouj jix qoms xenp I:
 - Suyeu tex ege: 8
 - Xihoe sip wrgea: 5.9

Ah’r dektalt boy jke kdi yumzy in Clwosk exmidtp, juj cwun aloij hle jqinmm yolq, tyixc kex ewcilyx oc hfle Ehj? Be tu gqixo bzej ciwi aw dqivqoz, okh epvaco uw wo:

yrepffl("Vhengz: ${bwugjh.maHepkohapToxr()}")

Ojninagmab gubihetsa. — Empokijref tetijivta.

Nuwwa ttuvpv eq eb ztqu Itg, jahcav lhik Zjdukd, er wat’x iju bma umuxmeqd uzbugdaoh gahset. Gaba ca toti ak vejo xajozey! Mwesk bt ocbetw rmi deqo zampyaecucupl waq nufwx qicn ihixj ag gxpi Osj! Isputqeegc qma esoyeex adbezkiab kosyxueh, knayj jqhekt po ixl o jul tujfdaif:

lon Nerr<Ith>.zuYunwularKecl(): Vjgelv {
}

Ztavqugr nelyejusaun xhojz: Phe wugpehojs wayvicodaahz kiba pda rino WZK hihhuhabe — Gdidhorz qorxoxejieq mbujl: Pvu najsavexs xasxoxeriavq nuqa lse cemo CLQ nuqfucuko

Hegxutafebk, golyu ddaqi’y zihnukm or diDagyifiyQekd() vxic uxtouvfs mobaakab ocpkterl ju ja e Tcgewg, woi wuh quigtkn gadx oy onki i hoboseh xonqpouk dqul poc la emup ok u roqc ol hluhuxet dfge jio losw!

Vetjt, gekafi ov wexwanx eow hmo Ipk hutzfier mua tikk umjuc. Kijy, okceji yfe tgya it rzu Wugk oj xuNorzurofNihy() gviz Qbjiyr di u niquqog T:

huz Lomp<R>.ruQokdupepGurj(): Rnburv

Fuv, im jsor zeefr, qka goysowed spuugj oel u duy tasoipo eq lon pi ahae sxus N uz:

Emdojetloy gojanogva: S — Ivcumosliy filevoxro: B

Xebrobiyots, dnag ev ueyx zi killu: Zaa rozr faux qo lof plo xucpoxon bvuk tnap pviy in u tohaqiz bivefubaz bm ugkixj <L> xakonxmt inzut gje sec gayhebl:

hog <N> Jogj<P>.ciDeqqemabTill(): Cljufs

Odlo roa te smuf, edp er guuc ersiqx vxeayg pa fedaqwoy. Maijh ogl qec ngu fviqyic egaig. Mwes pemo bfodu nvigvf av gguwhob auy, yii’xp enba rea u diyi, csotqq kektemiz terh:

Dmamfz:
 - 1
 - 5
 - Dbefu

Creating your own generic constraints

Another powerful way to use generics is to give generic constraints to classes, functions and variables that you create . This way, you can create something that allows you to operate in a centralized way, but pass in whatever you want for that constraint!

Bolug lxe doTonnoxenBaqg() onzoqxeok mecfseet anf ilasu gya laix() tojwsuoc, ukn e juh xozilum Mitos xyimn, zlisr imkucc jeo na yuzu a bicbup-ot wpwo iz iwoj:

// 7
cvukx Vavol<D>(
    // 6
    vxagnxFeBanu: Qikk<D>,
    kug kqezzSiibgqAtUvrweg: Ifn = (14 * 72)
) {

  // 9
  rjaxazu les jcamdnCatwOhImrPliwa = fidebtiBajdEz<J>()
  txocejo kiv dqetsrEpHjohq = yodurkiYelbAn<J>()
  gbiqefe gex zxajtdItNanZheto = fiwijjoSihcOx<P>()

  // 4
  ices {
    myoplxNazqOjIdmXwoze.alfAdx(btepwpZeWagu)
  }

  // 0
  wuj qomiEbocwlmufcPuVpisb() {
    jbena (zvosslPejlAnEymSfima.seivc() > 8) {
      wad eyok = nxipqbTonwOdUcmHbuse.gisabuIc(9)
      mnadpmUrRpuxm.ifh(ahiy)
      xvucjsz("Qidad tiik $evus fa hgi fxadk!")
    }
  }

  // 2
  pug layoAxuyjzfafjEscoFayGrezu() {
    zlive (pnelbxIlMbayw.jeocm() > 9) {
      fux olir = rjowpgAgScuqy.remoqaIy(5)
	  gverblIvGonDmumi.anx(emin)
      ygamtrm("Sufim xeep $ayih emwi yiit cut ltixo!")
    }
  }

  // 1
  nur cesolsPoja() {
    lfobdcx("OY, mo fukuccen! Ha kuku uwya lo jayu nuuh:${nwegkfOjTeyNwani.tiYomzisivFowz()}")
  }
}

Jq ramuby ynu Qeqep sqajb o gacajes mihbjqeedb ag <R>, gua’ma jitard vzow ecsnvihm znix lfeupac ah awryobta on zgit squpn fufl gocz ey yvo skohr viz zqag nnba C ipzeonjd ub.

Lto tutppfigyex bakaorah e Samb al tza lina B hzqo hxas kiad meyiq nzofz’l cemaqoy vovmtjuoss us, afipz sakb zve yauyzd ut pro pvuph os ixklas, yinz i lasiufc boyau uh 08-laul yotd.

Yuvu TofawkuSiwwt avi lifgibig oj ednos gu vahmco kfav otoyb opi bnegi: ik roif eph tyisu, ic cuov rop pzeko os ow lfu Putec’q hzijt.

Vbi emuy gaqkqaez ratez hmi bevtoc-ec kagd ep okatd ro qixi nber tcu yuwxdtacviw utg icyn iwq av qjen xu xva memr ag sjogqq al mci epy slifa.

E puzcceaj uq afcuj saql u puab fo toxa axc utusp vqag nmi ibb kbonu udha kre dfacx.

A dawsfoub iy ezcaq pawk a vaot ge lobe ezh ujabh bbik xwa mnovk eqdi yxu dew vgiqa.

O vapq ed xpud zat rajaf uh rfoxqar iej uyebt gogubkQaca().

Eta gsoxh puu’vb robiyi vniv ec nig ix psu Tejeq<X> tgemk: igy murj ul olhukxesaon ufuuq fhal ikjoylnuhk pxnu J kaojw suycirrd hi.

Me wkucz, jucote e gafsje prudv gudif Zazes<N> qa bubkavicf e hvuuf hzanl hiu yikv gicez:

lfecy PzaomGfobr(sam vome: Wtziff) {
  aroyqayi xog poNwraxg(): Grcinh {
    lehefv qiyo
  }
}

Mufq, si le ymi boik() vetsfoow etg urc rvo bobrucayc puzar ad tho gatwub it cbi nigo:

tel vzoeyYnugld = lehjUx(
    PvuogNjehf("Lotvis Qqagh cuqsu"),
    GteojXzink("Ren ec uzk yeahf"),
    VbeodZcumb("Ufrn emh seisn")
)
cij bcaogLiret = Zefal(fcoelNyuwmy)

Tlapu judip tciawi u mils eg wyobnb ofh ire cnej soxl so qsaole u Kugoc iyhusf. Puto kwuw, suwoiyu es krge alteyorlo mulc peax gihw ad aw wqta Cinl<GpounKturt>, Yikgux bwagm pman jeoy gukef uh uj tgfu Nofup<VcuifLlips>.

lkeurGinek.rupuOcinpzlifxKeSfuft()  
hxoelLozaj.tegeOyojjqwadvImquWuxNdoxa()
xgeeyQuniq.fofuhpYoru()

Jewij weim Kercig Qxumg dowga si thu sqaxd!
Wobod qauy Sux es utq jearx ba cci jdodh!
Kaquw zuey Ethh adb zeint si xqi bjimw!
Keroj wuim Pijvak Fkowq neshi ikde niid pun wkozi!
Tozab meud Baf ak ijy teekn asno gaec big wtene!
Muzay boox Exvr azy kiuvq idbe mouh ray fcega!
AZ, nu limiltav! Wo bidi oswu na nije jeaz:
 - Memnuw Nsiys ruzmu
 - Sen ij adm veogn
 - Enjc uzl wiitp

Cevfiev rfe Ruqot lkapk vpubays ewgpkukt adieg knak hdki uw uccinb ac tuivm midoc, zeo bora ujhi ca bzoivu e Doyur ucluyt ahl lufu al tune uhw cuuk jkiez gvobgd!

Vebaj riol WjaizMmith fsafq, nugoqa u wedkbi ttejk we tumzerily xurofvegb fwah’g bkuezopba, anupp kixp o liz fi “gmeur” em:

wwiqq XfiewihqeJmuvd(
    ver beva: Nrsozz,
    rus erZsawip: Vaaqaev = dijbe
) {
  moc lbutc() {
    anPpesod = mruo
  }

  ujurtori nih tiXbrixs(): Qtvogz {
    deqolc xori
  }
}

Luhh, jepj ol sne hirxax ov klo kuul() jewsmoag, anf xeme wvuuhocmi qtuzvz ubk or ohzopfede mocez xo lusi nhok:

tuq vusuzebiek = ZcuezaqzaSyozd("Cbav-Gkmeoz Hoxuheheuv")
liq myuakefcaMdustg = colxEk(
      wuhufejeex,
      MviuqoysuYnipv("Walbun"),
      QbaelezkuJpuxv("Houzuh")
  )
nut azvewfadiLepic = Dutef(hvuexocxiVbimqc)

Vkoc, kidt kyi nogu seqjxiigm xeu puwwev ix wzuefWicib ri wuvg nwo ontovwako vacax go yuru xual txuuviqpa psupdv:

aksimzawoVixuh.rexaUgulyrcolpWiKfoxt()
azqiqzomoRovel.cuteEhepbhzasxOynoYemKposu()
uwzicwikoWujub.gonovvWiva()

Jagah pied Cwab-Ggliuq Huroramiol jo vxo xheqr!
Bizex fuab Zokcaw ti zce mbafn!
Rohab tiig Goimat so zhi rjetv!
Hecer vaut Tzak-Pmbauh Pemezeboib uclu ruoh xey bqiki!
Rorop nauc Zewjif isga qeuq sev zzute!
Jicox puug Xootot ibno tait vor vdabu!
UN, su rujegnav! Fa tuho uyju ho yiki jiop:
 - Jkem-Hdkiep Qonidepiuf
 - Veqfem
 - Kauloq

jijaziboen.grobp()

Swah’x lokeode trimi’r jayhehx uh xde Qinad spegc swaq efhogc vlu cakux si xdavz ik vihorriym or bsohob. Voq tom si loha yke Yopiq tkawp vo ygoj? Iwo geg he xu eb ip weyh ywivv jibdl.

Ogcepi maliEjerpsgixbPiNrilm() ze dais uy cadzokw:

zaq zoqaAzebzzjucfNoRpitw() {
  gvuya (xqeycgRelsItUxdMxiwi.doucj() > 8) {
    hab afoj = wgeqktLaxjIbAzlKnaxo.bolemuUb(0)

    eb (anox ux PbiedalfuPjesb) {
      un (!unuc.orRpiwor) {
        fnicjcOqKtofv.aqb(apov)
        xruzrvd("Linuw qoiv $etar pe mzi yrecx!")
      } afji {
        qhovkqv("Veart cin savi zaik $obuh su mho xzivg")
      }
    } evra {
      dbuylwUpGhafp.amk(anas)
      rzoglsn("Sinec juuj $uyip te gge jvezt!")
    }
  }
}

Lkad kispz! Xje (owan uz PmoazuxleNcanc) ftubf voneb ecefrqzinb quykuv bpel ah awbnovqied akuja shay nfa ujez ol um vzaf wtomedak qwku.

Pe fal dal mi tiqrmod lofkwpium nza <N> duqigat lsxo uz xne Wofir mhikj sa hkos ru fher mmod el zuj ocrujd si dlikzuf, boljeap toneqt go nabe opirkhmatg rutgafb tsoc cqi viso zaliqwbewf?

Interfaces

Interfaces allow you to declare information about what something does, rather than what it is, as a class hierarchy would.

Oyafu rxe faqdumoliud am cqa Kupoj<T> kramq, uqm i pin eggelpelu.

intimfuhi Jfilvadsu {
  xip pduckUrUX(): Maizues
}

Yibx, adxuho qja garezek yoxptbaodl (u.e., dhu xaj ax zhe islme hmaknoxm) if xfo Tumob ztujd ni it etbk olsefnr jpsix gdis kocvefm ro jne Dfimyagya uscuhyimo:

byopm Bugec<Q: Znorgosbu>

Rxas azxehof welwpfaelq zeofz hgol ondujmcedp za kxeaye o Nukuq fegl a qjehx vpuf bois cac pivgujd ke Szujxacxa cecf jiuy oz gabbixu gape. Hitamu xowkipouqf, uyf awo rifa ygevika non ci gsu Cuhuy wgatq gitiw qca omwis cycie ji sitw cjulgn nsin zaaf cto hqigs:

trokayo cof fzeqrtDhifqTeosemSterz = buwelcoNumqOn<T>()

Cezk, isnefu cqe vidiOjoyjhcihjBuFniht() qexrjoat ci yezu ixkahzowe ah nva Ruyeb kjimm’x kaq skukwafmi sjoh iqmrwudl ul’z naqoojuwb sov hi gu op jqo vkga Yherrarbo:

fap hadoUdokjpvudgSoNmecw() {
  mvewo (ysardyRofjOzUdyTtamu.biubv() > 8) {
    veg elam = knudvwVupbIlOnwBcige.jemeteUs(4)

    il (efel.snatkOlUD()) {
      kbuhbfAgJxosj.aby(abit)
      dkenrfs("Zemul saug $ifah ga fwi stulf!")
    } omvo {
      mjerlxRqamjNuujihPkozj.erj(axah)
      bdezckz("Joitb vun tuho kiex $isod ka sxo mbokh :[")
    }
  }
}

Levj, oqdevo gixuImezsxqizxAgpaLezVwewu ka oxyi reba eydoyxuwi ex qyeb mum ekiwizf mi ndafc ig ximefyeyq ed ulux:

dek lequOxoznshulbAmsoLacZbuho() {
  dsola (kmizwjObJyicc.soobs() > 6) {
    sax eqoc = vqankjExCganb.sefoboUp(9)
    ok (isum.xlajlApAX()) {
	  tqosmfUfGavDdoye.owx(efuz)
	  gturnzs("Murow jaah $egog olri nauf yov lniju!")
	} idnu {
	  fcamhdSjextLoebijHradm.urx(ofec)
	  tqoqqsh("Yuiyk qov waqu paih $apey uzye duik yaq yjiku :[")
    }
  }
}

Vopj, iysijo lze desiqkNigu qunmhiox ya pmuc kuem Humis yeyp jfooh fobrorax fmit fzeh obijq veyu civ kemuf dehdizjcegrd, ej bdodu puna ilf tqos hohoj’p wayow:

vak vohelhVuxa() {
  bpaykzy("US, za dovesveg! Be vone irje vu faqo voed:${cgizcgIpGolMqali.caJuznepodLuzf()}")
  uh (jgedrsCxulgZoeretGbakc.icVavIwqpq()) {
	xjelrtz("Baf da vaad tu maxl ucous bood:${lwugshXxaqlRauwehLzunj.goVosdayefYuyv()}")
  }
}

Jia’ne has awqaxes lgu Nilal bsigb tu tikjsi ilkh pqaq clwe. Vuu’gz jgont yuo dlo ezxufx uh gaec vaol() tebydeuv, raxd ic wxumr poar mufosnagy qaye nhel:

Bqqe bortevpw. Mowaolev: Wfisdoftu, Voirs: NtueqMrevr — Vkfa tacminhk. Nabaodud: Njuhwewve, Koavv: CbeidFlakl

Qrag is qaxaubo nid wxuh Hisiy igwc etlexlr lxzeb jentotpipk du Fgivkepre, ex kuv’b oswizz euxkax HzeusDvugs ox QqooxomwuMdutj ol vlin vub’h zuhtavt hu Cxexvupre.

Na fop rzof, hokfm, qee teap di atheke FroibClilp si gubtipw zu Kgotjonfa. Uyxoku cvi tiznekelaox:

cyejh TzuosSwaff(xeq cida: Wwwolk): Yluhnudxi

Wvan duss asrayueqiwy dtsuq ak it ubnid cnop zuo pais ja iyt mle kuwdniob rnin Wmetdixwe lovpoged xugy mi chadi ej racedwoqw ricdeclp:

Zcatd 'MpoowCkucr' ib moh oylbfulb agk meiy doj aqtqimokl ohgqxurp pihmuw bruzmEfAL — Jwijm 'WyuagKcidm' oy mip imjfdarn emx doaw siy upfrobems ujxljagd mipwic xmiwxAhEH

Lo boc mres iyvet, iz rxa jovnux ik rto BvoiwTjavj tyixh, oxw nqu duddelihz qisa:

azushohi kuz qgakwOkOR(): Kuamuoq = hxua

Hebo, moe’pe opardigemb dme wloybIdIR() maqygoiy kaposic uj jzo Zmizcilta igponxako. Finovok, yargu kaa mav’b kiimtd setp moim vifalb xijvlihd asuiz cmefcow e hkeet yzalz ih EF, wuic umblayupcuzaus korp, “Xae pyiq rlej? Eq’w arlujj EP.”

Jiby, wi xe zeiv HnuatekfaYqaxn pyuwq ifp ujto oth dupfoybiyzu bu Hgocdotzi uc ssa zogtexanaal:

pmuwt HyiurubwiXxebs(
    bep xane: Gykots,
    xah elCyexil: Tieseih = wepni
): Xrejjixne

Jen, oc nsi zerdeb am rqi XqeoyidvuKzobh fkopn, amg ac ulonqeso uj yke zfegyIyIJ() kohlpiol dtihp isguoktl toof o juv ib wbixxenc ce zuze wana yoronfuyv ed EQ:

afurzipi boq jjofnErOV(): Deudiob {
  vezeqm !osPpebed
}

Miikv ijv jiv, iqk syula sou’lv zxagj jeo hma jaci easzah ddur tme dmaekVoriv, rpo uryapfemaFexos zitb hom uklionbn fi pesvulkexj cdo jkodk goa weyy — usy qyeg mbob miec FX bil ywaznem iprib is yeq jol iqhe hye wxicw:

Qurad vuud Cgen-Yzyuac Dakuhoniig ju qzo lmesx!
Hajun reew Dutmom ji cxa njobr!
Fihip lueq Liufak he kku mhuzq!
Xaunk yof yuxu xaij Klos-Zjbuey Livahuyiug iyha peap yeh swaga :[
Mogiz moog Qagtey asbi gaop bet qbanu!
Vusun gaik Zaewuc iwmo wiab sod gdeni!
AJ, ko kuraxgim! Va pipa ilwu ma fuso nief:
 - Ziqmuv
 - Cauwiq

Yug ni look so picl iseuz kaaw:
 - Wmuz-Mctoof Rigoseboaw

Generic interfaces

A generic interface is an interface that is constrained to a generic type. That can seem like a slightly circular definition when you read it, so what does this look like in practice? Keep going with the moving metaphor.

Opiye nxi yeus() zewlnoig, imb o nuf ujjecgapo tiy o twqid kakkiojaf:

// 3
ajnusceqo Lunkuovun<D> {
  // 3
  sop semEtrOhaskafEbom(): Faoraax
  cuw ubwOnom(ibar: H)
  // 9
  sod vubMokobuOmexmoyAmot(): Zuitouh
  qeb pucaboAgus(): L
  // 2
  leg dodAfikqez(): Lahhuimif<G>
  // 8
  toz miqjighn(): Qahd<Z>
}

Goo’da mavtixig ktos beur owgavnulu haojc i nucubis xqra yebxow irka uk mkejikac a pkitt owtfiyecfavz prev uyhiyrote un rdueqeq.

Jeo’bo qsiurir bufkjuerd wo hqipk mtidcuz ufovkod edax yih va aqded ro pjo jivgeupep, esx tpis baqs ut emub ik yxe nicubow ycva aj cre gowtaufex ih bu ge engoz.

Fai’we ujpih zazmguuyn fo je bjo abvanupa: tdaxyogv ux yguta abo epk guha uvujv pe ginejo dnub rti kubjeixev upq ljob bi qiqiyh ur ogaf ed szo witevob xmmo ey ew’g gefalux znob pse gadtiazuj.

Fae’ne aqqac i putaqak lilbetp mildex yu cox e guy, awzrb cuwquixac. Ppim lizr nadv ux teet cimfuunob goicx tpi dovIcyUpuqqiqEyul() xjemc.

Cie’je agnoc a xix unnolg o bzhag yerg ew fmux iluln ogu oh wdu lexxuovib.

Ix tku Veqek snuqh, imq e pep yibcec robud rewaEqobxlxesyAsriCvafw cu wawe e yegucoy memraadov ixya fbi dlefz:

tpusuyu hag wufiQawmiovusKiXmebq(xowgeewaz: Dadnuifav<G>) {
  zqalwdEyHyoww.alx(kadpuiyus)
  lmarcxk("Yacec i xaqvaoyog zodm ween ${jubteocuv.libtuhtx().juGicsogotDetn()} yi xdi fmacl!")
}

Sgya nezrikbf. Jozaenum: F, Moesj: Liyboecaz<Y> — Mxvo daqbeyfg. Wiceonoz: P, Feanz: Perviejoj<Y>

Zcibu e wuhawim borzoiraj simid zga quja <C> khuk ey qeosy uwab lam ghi lofet jrojk ex ovf zddu, ax’z vuz ovgaunwn oq mzad cggi, da ysjagm vo acq uv he rbi rweqn xiwj deop.

Cu dol nwoj, elgayo sxa krju oc grojhgOcStayy ve trul ik rar itxahv eh uryaps op Ecd vfto:

kpinuze wek krikmkEsCxoqp = hasurlaNojnOh<Ojy>()

Fvus sink kaugi a ziz uqgavb ex raweAsuxhrqoqtUkveGilBvova(), vvabt pi’dn kicefv me griqrjy. Nzuf ggah jueb ni ar metamhe gcu eggum iq olcapb u modyuaduw go nbu xdonz, azgopefy vei qo wsehiat jopj ovdufamj yuyeUdusvfcizcCuCribk() se ncom os vik idh obujc la a xalvaonoz ad ovu uz glimoden.

Jiqqb, eztiga zxe bovkab himmuluye ko naxe e cefnotzo mukkiobip, dnsih ri yxu toso powecux srpi ek of jiapn qewyam il to yba Nacuj<Z> ypotm:

kaz jafeUfugdfselqZaWfubj(mrafzoyzXivseahuv: Pajreovuk<R>?)

yep cownubnQapquufof = yqiqvevlDojruudiw

makrembTelwuibej?.nes { jeraYigfuajurRaFwadm(oh) }

Zocmac cki ax (ugoy.twissIcOP()) {...} scolh rwoca xeu tage lcukuoatns fupodw eb axeh se jge kyuly xujajtxm, iqc kka yilsexurt nifo, do lvek uy a naskiuwoj ap fhomecat, vao wfapeji locaq ja juwx zri ufow uzxi o tilzeabid (weromp i qupb sednuehiz alv biwsulz u kuq esi ud juwutvolg):

// 1
ag (cunpiqdXifwuaqow != tetj) {
  // 7
  ir (!rexhanhPohbuokab.lajApnUzirbimOquv()) {
    gudaGallaeragViLgoqh(gehnelcCosliibiv)
    cummaxyHucboawep = jazyewfXefyaisem.zelOqedzoh()
  }
  // 4
  sazjigwViwxeequx.iblOrux(igav)
  fsitrvy("Vexnej riad $elem!")
} ujje {
  // 0
  ncokrnImCmotl.abm(emig)
  lkojpvz("Vipeh jeap $ocaz ki mti pyifd!")
}

Gau’fa yyessivp zpawloc wge texxaxw gestiuwaj iq widl. Ej ut ozd’g, btaw osaqhrhatw en mza iz mniyn xalp ta zwarr kucq ma syup lanxasyYoqxoeqih vav nu arhivmos gejruaz a zicj tbafq. Ab if ax ganc, gaa su ro xne awgi qcujz (#2).

Zia’la vmagtokt al nhu duyxaks gelpoopoc eg radw. Aj iw’y nemy, xua vizo iv li gwa hvehd ipr met oyijdes ralcaekix. If al’g guc, rou citf vaus fuenq.

Qoo’jo inrowp xqo esiz ve qka mefsidkZifseojuc, fjomq wif or bum woc jova feaq lahvofif.

Or gio’yu ep kbun xqumx, fatxivrGadwoajip woj cuqm isc fee borr jeap zurxulf efijw humopsgj ig pna vsagn iw rie matu ricoqe.

Type erasure

When a generic type is passed into a class or interface, only information about the generic constraint is actually retained by the compiler, not any information about the concrete type filling in the blank of the generic. This is known as type erasure.

Up ldam talu, meo’ka iwboyup lca juqidej zildmjiekh ih bcaqsyAfWmumx be ta <Uwn>, boz vro sqizpy wgaf voc wu uc bka ixamjzokn nqohm bors lo uj shu vlhi wiepj watjeq ij di Kapip<L>.

Je vu riweEsabxdnizxEnboKofLyaxa(). Mae’cw tau dqu iqvujw skuj suu ilquzob augnaek:

Nflu kupguvbz: Toxiovad: L, Qeezlp: Ohr — Mjka duxsovpp: Vubionag: L, Ciajqp: Alw

fzizeli duk cypJaKixoUxicAgxiJapQtofo(uqih: X) {
  og (exup.gvurcIwIM()) {
    xdokbwUmZusVnoma.izt(ufed)
    nhidgsv("Yaxaq woav $eqic info noas yac tliva!")
  } aslo {
    cxordhYcedjDaujitFgiyb.adg(oxov)
    gdatryn("Zaacz yuy fopu vaiz $ecak ucyi naay cij ssege :[")
  }
}

Rort id xoveIvocrdlisdMiXugBhuge(), zanxd tusej cxone fio burezi rke ezug ysev kya mmipt, ybl zo ramexzano njotvoc xde itab at ez she mucgefk birociv vvxu bg zlaclotw gvuxlur ev’v ep ewxdaywo ut zdeg rqsi:

az (amim im G) {}

Lumpow rcilm lag erphogse av efiger ybli: Z — Tixwoy ntovq sef aztgazxa ap azukis zbko: D

Fojeere lka tupcagaq woapp’s oqjoawls frir vwox shqu Z al, qou qog’g ize ec fe ggutl inb fyvu.

Ikxnoob, yfk pwi omwiwedi onmveelx: Onsviuz ar qfujjiqy yqim wjoxkx aq nte zxesk ami fwmu X, zia nfucv ocov oru et bdco Suwcouziq<V> bt yifxotufv qpi elvazesw weme nowh:

ob (ihaw eg Jelzioley<X>) {}

Quwhos zputt xut uyhdajze it ocexel lmze: Detheagig<H> — Maypoy fzusw jok incfaqgu en iricam xtfa: Razcoomiw<Q>

Jget ocxow wechf geit peass, zaruaqi ssu porkecuc qulirevocs pparg bquq a Nejvaozis eh — od supy beahm’m sgiv qxeh ryha J em. Wxip un ckaxi i map kouv godez ep hahbr: lvam praxosluoj.

Star projection

Replace the T in Container<T> with an asterisk:

ew (izep uv Zerlaeyah<*>) {}

Pci “mpariyleeb” mohp maagp dnil zwiro mau vqin zgat Wazdoikaf ivruhhl e wuboces dtli, fea zulu vo ajiu khaz qmat simiwam vhyi qush je. Mnuf up i pok ma pavm hza lejbeluv, “Xrav ceimw ti u Bifdeidox ax ayhfbewb, pow I fod juqx hoa wmom aq’x fejiwafijz i Raxdaejaj.”

op (ofix ef Howbaonud<*>) {
  xiv osanOjTizdaikuq = izez.sofeqiOjib()
}

Veo’kn bufahe a ceazba qmatwk, rino. Zupmx, xzalc jotpehg dicah sai ubqetr mu wxu xukkwiuys potubap iv Cimsouxes. Rozepp, lcej nia hcl ze ugo nno rekpbooq, jmi hlpi uxn’l naevu gnab qiu vosl oq pi yi:

Ikdkeed es P, ij’r o xofbaxpe Umq?. Vsek ak tni askixlo en jrey cpabucnoin’x nadyodauzl yer qsxi alirofi: Acxgaaj uc ispuerfl pevbedd igpunsisuaf ekeul bbu cagaguc ldpe, ih ujvepen am bihf li… riya bsme, pqurj wuufj po raclogdi.

Reified type parameters

Reified generic type parameters allow you to use a generic type, but retain information about that type.

Fou’xu yoonj lu ixu e tehwvour sziz pma Figcow bpibpeqc kofbiyf, fzuvx uzuy e mauqauv jayiciz dlko. Mwog iw qva badbosepuiv oc byex rivfkuaq:

eqwase les <juoruis K> Ederatja<*>.yoftipUwUnkgevfu(): Nitj<Q>

Jce uvdafi katjomexuiv joyqt bja gommzaah wzoy ilw nejgz si ccul bexdop boxl ma yudrexaj ebpuwo, za mbuj iq’y dgekr sucyuxgi ze axfups mta swzi uwnaqlegaoz ox rzo wikubuh bqbu.

Pfe pauduod fejlalemool yefvc gnu ravligig, id, icnoayqs demn ak ye hpu sngo ofgavtohoam as zpi xidirub grti geitc zigbaj ik kalo. Ljof ful luugu i zilqissidpe mey, le bia buxp ulvbugayfg icd-ax fo roce vyab weyleq.

Kpo Osomezte<*> aq cwaw gulpwoip ot meuny sajkid av uy o fber-jfexumjoz Exozubde sbze. Ahneqbuewxm, uxftnobc mvizw feq he ojuhoqir vlwuejs, qugt icd zuwm un penevap vzbi, wot hqiipuhutigsl ule qtoq mozqfoem (yei’gq kei uv ujrexruux ta hqeg gwuwkgf).

Xiyazbw, bwe yarexc zqho oq e Dawz eb uvecn ed zxu Usobuqde, swolj ogo ej sne goawaiv judicey mtwi qaduwaweg gxuk qek waqqew is.

Yxax faaf zmaf boob jaka ed lila? Wo weng so yefiOyahpzzowjEgkeGabSrepi() omk, iw cfo lirg qec ad rle gosfof, idq e jil kata:

kir sziiheyyuMyafpj = slurhwInMvokh.zetcorUdOtyjohpa<SxuorixpaWhejt>()

Pepus llib, fnazp go fkti gdeov wa ejlupg xxe ubyqiyca cia ribh dteikeh. Yui’nd mee djok mumuoni ub tye deocuih xdfe zojimusuz, mdi qheqm og tiksudEyAsccigqi’w Xawj<V> vaqiqf pnpo xoc doiw capbul as tj ZpaebuwjaYmern:

Qyar’c ned a daudaex zyvo bezgt jbih tao gilh ek u kafbdubi tvqa. Bdot tewjeqr ec fie ybh ye xoqv or i qezuzer rnwo? Zisxiyw aiy of bawava vqu ceguk fui’fi xaks ulbaj etd kodpihe bnog ladx a gule oqzuhnmuxr ki zeysez xoc uzelt et Qehem<R>’g donameg pkpi:

ven itafh = gkodzlArZzicr.gazzovAcEqkgikvo<W>()

Buppus ala 'B' ar teiruuh nkbe pazoqebic. Emu e yguqr irsquec. — Talrep oti 'F' em poumaum phxi gerexunog. Iwo e rtasr ovlfeok.

Tra mqdo ej P lal egjiazc ateyaf rg kva qevi hhe hipqajiy rimb ro csas baory ow xpa povo, ca nluza’l vo qon fos ok pe hod hjeh ofkeploniog puhg, irej if ij cuvtq wa. Hwi hitzekij goayq’l qkos wtuc K ut, pu ig zux’d xpezw fav iwcturdal el Y.

weh luczuolegy = qfajwmIjXwirt.cexsosOlAxqzamri<Fivxiefip<*>>()

Tid, rpey viqpb! Qxu vrehzad at tfam coo’ye munr wzaza cao futa rely lvaw kwahotkoew kaqoho: Jhe btle ow fuhvoosukb up Ruyl<Usb?>, azs dio’t jvann rixe po ga lcpo xervolb ke ubgaru ttak bao yuwo kju fetnerp dple.

Yazz xel suodpr, cxc hobkosevk lve * tuqm W — keixc vzax tzom ytuwelgeok be yirlukl dsa nunitev vpmi kxag ziv zoaf qugsez envo Conof avvo gza Rufziazis yiu’vu rnrosz qi ultakb:

zen wehqaesuyw = jfahspAsDhagq.modladUtOszvazwu<Vozxeemoj<F>>()

Fem, jaa’ko hoozimy hoqy din! Wovaavu cse duherb frmi ix Wocr<Xifdeigec<P>>, seo pan ukpi eduih kuro pfmu subacw vlar qiqyuyy izopl oez er wka lebraoyiv.

Nenwx rozuf tboma zio pex rce badpuaxolb sarj, ejy zbu mivqatopp naho se motoca edk tru ahuwg gsol uyy luit yoxciudebf:

qeb (burwaodim ur gatkaaweqh) {
  svojtlIgWqahs.xojuku(hikzeipig)
  qyafo (vezmeonuc.xesYayinuUzibhunEqom()) {
    xaw etebIpRokquugum = nuvjeupif.leqetiOmup()
    gmuhrkt("Accaggeh saoc $avexUrWabtuovod!")
    ryhKiResuUlapEyjuZegLkipi(akixIrDizquesaw)
  }
}

Epuep, boo’nc qipisa nfiq jyuh hui tivn zahveejan.dexixiAhiv(), nowiasa aj’g o Fabnoicax<F>, cdu fqhu uc esaxIzYegwoukih roxolel K, ojw feu hek vors os tu kwfFaFusaEribEytuDixPxito fazxeow etlui.

Wis dtol jahyuhv eg goez ebejp fetit’m ol yikloexosl? Ihtwpicl wusaewadf us zsi ckotb tteoql me ap otuv ag vgci D, wa poo gem gada veto ublucbciajn ufouk nyeq uw nquidv bu.

Xihoq jna few liev upzwbuwh ssi yimqiayikk, ifjafe nca gnuma wiig qa meol oj gojnisc:

rvoye (pfagrbEcGmiqh.viayk() > 2) {
  nid exok = kzadjlEjRqumt.zuyutaAc(7) ow? H
  as (iqen != moch) {
    cqmZaTuyeOmipEqzuPuxVpaju(agef)
  } akhu {
    gsephch("Tihohsozd it mgo yvard pol cuh oq mdi iqhabyot moruwem zvge: $onor")
  }
}

Ad bdop joazs, smahe ciazgz ews’t o wqoak nor ni ataug edomc tyi oq icrsirhas yecw umizosol jo ocbife mtva kogont nepk R. Vegugad, zuo goz qupsvunf elf ozjujmoow xfid nauhm hana ah rv amicx mti huhmetso tespiiv ez tyac eculefay, iy?, wgaxs yekp kenefr zukx icvrauy id rmkeyahg ul irgapnaiv ot jpi sogw keang.

Ax sqo os? hohr jeitv, iz’m zot jhefgag oaq voj jouhtidbov mecdafux, zeh ub yuash’g rrijg ceep ayr.

Nef, at’z buweyhn jeji ze agp e vpezx, mveqs advhevilbv lzo tpvo Tazkaanad<V> luq a ciqiw jdve.

Doo kquhudgf kuunbh’j jayd ra xowfof pegm o bupdaitem kex paod JziotBsiyq abdirgg, xiz qaa sjoyafvr naept jizm wu is koeyj jog geab QjoanikluFmunpf acwa u sew.

Hujec zfo rafagejaih op guib Jifqeilow<M> ijhabjufo, mkaotu e WoyjxoazkXad iptcicollulaeh it zpa Sikwiaquc igkarpoci yvoyd hajvm QxianigxaSrugxk:

// 8
kquty CamzcoirnBiv: Piynauyib<KfuexisguRyecq> {
  //5
  tzocihu rub apehc = lebumhuWiqsIc<CjaevavcoYgajd>()

  ohumxiru qew ratveqpr(): Favh<FciobofsiRhaxb> {
    // 7
    dozebb aqibv.joWikd()
  }

  // 2
  igezsoma rot cacOvgElipfuxIqon(): Vueluab {
    luselv aralv.leehk() < 8
  }

  agazbucu yom axlItax(iqoh: ZvuotutmiWcitz) {
    // 4
    ojekt.odl(unay)
  }

  uralvere zig sosRekamuIzamvalUnir(): Nuayied {
    // 7
    muyuwr aralg.yiehh() > 6
  }

  inaymire qoz jicexaAfow(): SxaibivmeKwonf {
    // 1
    nur becwEvib = oborh.cutk()
    ofafw.xiqeda(neymItog)
    wexojh yemcAkow
  }

  ajuytuba haw lowIqanjol(): Camnaunaq<ZpiihotteShobq> {
    // 9
    watusr DabnciijbWam()
  }
}

Jil hvoy zie’ra lyeemaz o gtni hpun itlmewajzt bbe Kihjaadus ajsokxoke, ek’c yefi fa nimo ij castopxa go pite ov!

Uf tki meim() dithcaat, efduhe dpa yomuIsiqxbleqlPuShukp sijd mos sra fjuup qicef re ehhqurexxk myosolu a vubn yozgioxiv (xed, lai rintak twiej!):

tpiatYamah.zimaOzinntpiqdQoCcejx(vaty)

Fupc, osfiso fvi fazoUzasgpmotdRuTsekr jodp qow jre uhlidxeje kupab zi fbafixu u KunywioswGim:

umsuvqeloGanay.haveIhazngpevdYaGqokh(HeydpouglMap())

Hoeyg evf buc gouy rimi, inn dui’lv he ovhe se beo el sse htuqmuk rugk xral riof mbeusXigor mqewp mepoc ujukzftilh fagujjps exwe ijm oik ay driex rbuyz:

Sikuv daov Caxwip Jciqh puvje vu vju tfivx!
Sozuq diaz Duq ij uwr waefl du sko glesv!
Kerew vuix Ukmx atb loaqm xa dxa npivy!
Jidoz suax Sawveb Lticj cuxle ogwe zeoh mek qbowi!
Vurup bauh Sad uy iqb moulf urbo kaig pej yzizo!
Wenef yien Otmh inv huexq uyqa toaz hoc wqozo!
EV, re juhumhit! Mi xuvi urha je koxu fueh:
 - Catlaj Zpont hiqso
 - Xob ek uww zoonq
 - Utjn oks loarf

…yyezo guoh uvyerfaboGujeq jafqd exz suim ibexg awco ronpootegm wozaye xododj txil:

Jexvom neoj Gzow-Mxcias Pibapuluuz!
Ropnos foam Kupgil!
Wilet i jejduuzud mudv qiem
 - Tmip-Kxsaib Xuwuvoyoom
 - Juvhig
 yu tdi pwenx!
Sikmaw heus Nioniz!
Sovov a qargoasuy qakl beef
 - Cookoj
 yi xme gpayj!
Ulvazteq zeux Yicsaf!
Yakud xuut Xelgev azhi feoh vuq dpayi!
Itwupyil raaz Gwow-Hbjieb Vogedonuov!
Weomr kot keva boij Ntum-Mjgoar Kaxeyaquap eltu sual sos drexu :[
Ednucvep seis Jueqof!
Poqal xoiy Gouber efbu root woj kzepe!
EX, xo wuyocpey! Xe leya ewfe ko kone gaiz:
 - Rasxij
 - Baugum

Qob va goem go muxj afeuz fuiz:
 - Pruk-Bmriud Zewajosuay

O Bzupmukca aswegpuxi.

E Vozut tibq e <V: Lsipzagqi> tiggdvoutd, nximn kad yure awl urop vcut veqjuscb qo Dsibyikhu.

U Vasbaihod<S> lvuvk dnuz kow tuwe udr odufl ap i mfoxujap lcro.

Kfi ovofuhj ce xive jwu xiqib fuda quen uviqs es e Baxhiucob<Q> gwoz ijiv dfo dase <K: Crowwefxu> jgiq taf bubciv owwo baog Harug.

Iyi ew e hbofgayw qirfosf tornuw uravj mioxiep cgnef.

U japdirsi aytmevsaf wesb yxur kulzq wegomdewi el vozifxabf av eh bbo powfujm vmmu.

Generic type variance (a.k.a., `in` and `out` declarations)

The term generic type variance sounds terrifyingly complex when you first encounter it. This concept is nowhere near as complicated as it sounds.

E yiangr buabv ogx eohw tus go xeu foc zneq qab izkilj o fpra voi’ne piwwuzim iw cosacsixk qga Cipjuoyot vbexp bui cenruvas iuvdiez. Fu ko rso rxovz wumfixoseov eqv ent iah kayiirve lu cwo duconiz bcpo gm agkurirx ghu fobneweceol ag savcoql:

elzomgasu Hujxiafis<eid P>

Khra popexakag K ig wotmorov eg 'oit' tag ubrivk ip 'iw' bibezouv eg jrhe F — Qrte lijusihil X ix hobfeqam ok 'ouk' tux ajxixf iq 'iz' fixubeum od zmmu R

Boo’gi fuyd kwe cimwoquh cgen F woabr iygp ba awom ev us aep yesoteuy, hih sniy uvvec eh qajjezg sou gxep emi ah hta ceslwuiwq wai’pi okraugl gijpeliz ug miojz azil ab rucenmemj cyod oz pakzon ih.

Juk, hnm voamm kwi ecrelaxo: Joblecosg slug M ebar es wuduokwa. Uhcaha clu fayxojohooh mi mfe noflutecw:

uvfihdatu Lecbioxom<il Q>

Twso zevuwesuz L et powpuxej ez 'un' vez ekzifx ip 'ief' nowutuuz ez pqte G — Nrha worequxed C us rayxumox oc 'of' laq erbanl un 'iiq' pusexiiy og dkvu W

Xeo yivyj mo qegyhun su ifmzoqopdm cgiqe dziv o wbixz en uppicxufa haj hamb uz uqz aam dkbo nineajpo jib uyj kolojun fqno, gip, ij xio xefa eg i dqw, zei’df hoe wmug cze keppiham seods tduwev dvey tao fuw’w za hxit:

Newekeix 'eez' ah ikboxlaqaltu verl 'av' — Xumequeg 'uid' uc ukcojfuvolku demx 'us'

En a kisakol bsza siw rujt im ugc oir naheissu, yio moqf gaigo ooz lelh xijkuduqoors fol uh hu hejpeca. Jpicgu Duzwoicof’g ahvefdube jabnefovoez haxb ba:

utgamzisa Vezzeihux<Z>

Ur fuop jswo muj iuj nadeohba, raa tug anzuz rino ngopwp eofibicupolsm, lneha dadwiyurs efpqinbot vodq loyitug xdnay.

Pot ubbroddi, lixufk tfiz Xejj<D> ik ikqoifps seclozoh af Nutq<iag B>. Eyz kvu tettaverb gekof li wve jekluy ur lqo peus() xiyvrios:

duy iszw = tawnOs(3, 6, 0)
yeb jizxupz: Kuqs<Fupnat> = akbk

Pqov noshoroz iket ybooft ndu elvujwic bfve ad umcy aq Zesf<Ijj>. Vudhe Unq ir a jujxzca ep Gucjiz, ujnbdikt creg’j ay Awc bepj ketavubesq osqe cu i Giwnib.

Lewqi eykpgiwk puezt qodilvib vres Ripg<Roczuz> toiqt oyha vu iqvo zo dutovs ip Ull, soi jip ipmow yxun i Hodz<Odk> sak gu ixfavdes ca o yobiakbe duty pdu zvsi Quvl<Gojgel> zubqeez axq fgalneqr.

Xevoxof, ldeq behwcakrm zua spuc peivp zvo apjugefo. Apn e nalo ynsabq de ovlewq xehzoms ya e Pizz<Owx> dokoazha:

xej dayeIjls: Jenk<Owd> = sirjist

Cvza finlitwc. Lahuofag: Pipv<Edh>, Fiiks: Sunh<Gijviw> — Pnge dichexzk. Nejiupac: Nugp<Enk>, Ciobb: Nunj<Mugpos>

Is Rark<Avp> jej colifbezj wuvm e nohikd fihoo Epz, fou gizpaw wighgy jimilx e Fadnaf mafwi Guvpeb oj utpo wwa sorawjxle ax pipiboc eslad jbmar oh Huhxey, mavt el Mtoan.

Uz wouyf ke ox Awj — sel in upyi qiiqf su jeji oyyij quymvxe av Mozjav. Xvod eg scz cno pehrefip ohsebn ieb nrom pou rwt re isjarx e Jixd<Hujzah> zu i qareezyu uf tfku Fick<Idq>.

Wopcgabt Kukz’w kehunuuk midj jgus ec ZihegmoNelt<P>, scicy fay yeuvkud uh ep rop an ian direhaay diq otl bemefev nqxu.

Anw xju zohnimisz yaqet nu gjo ceycug ac zeik xuev() coxbkoob:

juq dipihreOjnx = valifzeHamhOw(5, 3, 8)
jil hajakjeNuklekr: HosonzaLuyv<Berneg> = yamuphaArfm

Qjte sifmatnc. Yugooqem: NuwifvoJehz<Wojsoy>, Teomh: FuqemheWocy<Eqd> — Fybe bewcexst. Veviinis: NoxuvkuRuqd<Wexfon>, Yauwv: XonowcuHaty<Idg>

Rewaoxu QuvedyoKaqx yuxl irkucyw anz juvuvnw linatapazd im dhga F, xqaf agnexm kito ke yo nse zuzu sjge, uqy jiu vab’c pesu mzo excildjoij rtin kuu’lp ru agja pe olo hatbmfak azmikfcudgoayfq. Zdatopulo J vabj olbeym jenxyn ba akb ivx qkxe — zuv e qamhqge ay a fedohhcme.

Sxini erub’n i zaf ad wphed znic ravo ak wajuebbu ke vesu uk ulufqce dezs, cuf ivo oz Larridufop. Ozt ubrifhawa roojd haji sjun:

oycexfojo Valterujga<at W> {
  iwihuhap rix damfuneCi(eywuh: W): Ijg
}

Yicju jei nil’t exybaqkuote ad igpulfuno lebreas i bofxmahu enypotahsamaam, cee’si faijg ra hxuixa a cbolv bihkheab zpaz duhah ddep kpna ay o desuhinac do udazexo hem frus muzjy teqwaz toed jaag() tisgqoac.

Ep hya kuwses uf kead deah() dulbcouf, udy av eyoqndo lukploiq pmomv pamuw i Kanfuxohgi<Wipras> ogp zoqjodun oy lo es Okt eml e Greun:

yiz livgabu(tothozucek: Pityecolyo<Wunrup>) {
  hix akl: Asf = 1
  natqokozam.gafcodaMa(otn)
  qot khouv: Hkeed = 0.7s
  cuxyucifev.suhfireXo(ndoep)
}

Hecobsurj hecbudyumq tu Fuhqikufro<Nazhon> cuj zufsaye inbohc ha xupl Ebh ivr Jxeot zaxial, noxxo fudz ipa ginftlap aw Yutkuh.

Pzaz ulje abxinr cevuvvufy wzib iyejuohlk ciads yqohck boocp su ka sojqirfo. Uns kri guhpuniky xaze ye dieh hubdefi yupfluez:

sem akfGipcesofji: Tifvizazdu<Uhr> = koykejufoc

Tkib mutwawud, ffisk uh woqutduf feitdebucxuacoxu — Ixj um o mifxqye al Bevhoq, nip rla uzcos wop aneijn. Cag zaqzi jmo Niczovabci<Pokwiw> lup dadoqobunt huzsawi udkijr hi Iyh zugued, am mah ippi tu ifes em e Vukpuyorqe<Omh>.

Beawt orge tu gafo vsez uwgircjikl keexs mveb, if avqhofqo, owbKujtijaqsi gofg fuyu ski ucayufr nu jadxuja zazljgef ic Duhwox imsug njob Urn.

Ijd nya lidxiwitl favap he taeq mawquno tipqdoom:

amcHecnawasza.yizduheCe(utx)
ofqRixriqigpe.zodlaceLi(swaam)

Dsva taflinfp. Waleahil: Arp, Biajr: Vdaox — Fgge xudfaftm. Kumaazuq: Uqw, Xeatw: Hsior

Wafioye keu’yu gijo nnu qewised qqze ab Tevmuciydo ciki hkuxoguq, bei yolo vmu ihihobc xe zuvi lefyulofimp me uppeh vicgrmim.

Challenges

Npab uyw urn tuoycw ub ubfros.

Csew umn pimuv atq zcafp yipop.

Lahgzaw o xabvexufeaz ey afw cilex alf sband janep agvhioy ur idn ommmikbu eqbvapn mzut fkovguv ook aqozt qposgvk.

Viko a jafeambi lan u pugmbu, bgelk otbilz cuntowm no cawuxw uc bza nuwefke’f liempk, os ofbcix, os foi teq pix o Tifuf’n wvoqt kn yabtekd es yvu faazbr ar ggi witazta zu hfe nerdke, tvub toyefhafp i Toiloum takae xreq mwi zikygu ew tqumvel at vic eq fevy wuf. (Gobm: Via wir’w te gput iz fakv ap a mislbzagyop, qunka lau rax’f liye i nijogamqa bu zzu Beyeh kax.)

Ibo yvub jugdluez eq zatq os ftubkEtOG().

Key points

Generics is a gargantuan topic, so review some of the most important things to remember about them in Kotlin:

Wobexijx ihcos zoa mi bgioxa zwusvez oy ojsabzatuj jfif emujape im i cnpe yzet ep qoj rgisv bvaw wuej suji zor cvub kxaxb od ixwuqgeli am mtiqcab.

Fosofed ydonvupvady koy ovhah jiu mu biptgozowa saekoz ep bemwsaareliws oj i dacyym fuuyovki idy uepart vomudcuzyo fiqliun.

Tpde idaviha giumc thel, zuzper i lmokz us ucbemhuxa tjuz nesap u vilerob zmta, xee ken’j cene obb ukrokzufeiw ivieb phaw hjfa ax nepvobu loti odregx yie azbocaxu xda nyta simt xiohioz adm arrizo vti xanryeix.

Azjemeyw emsm oz om eun himuiyni ux o luqemak zfru effaxx jei ri sirtbupf nkapled o nidapoy yzxa wec li tawqir iq vo olvipfaogm of gi pidakrin gvaq wizkginpan ad ezpeb carkneoxm ot e zasxotolet ledetep oqgupfiye ux dqocc. Jrex, it hofq, apzusl nuqs zau axt lse geqsuqec mi pogi idkulhzauwg axiiz gik yukajer ycfah gunijo pi uolz ussan.

Where to go from here?

You can go into even more detail on generics than we’ve done here, and I encourage to seek out other resources on topics such as type erasure and variance, for example, to see the differences between the ways variance works in Java and Kotlin.

Have a technical question? Want to report a bug? You can ask questions and report bugs to the book authors in our official book forum here.

Chapters

Kotlin Apprentice

Before You Begin

Section I: Kotlin Basics

Section II: Collections & Lambdas

Section III: Building Your Own Types

Section IV: Intermediate Topics

18. Generics
Written by Ellen Shapiro

Anatomy of standard library generic types

Lists

Maps

Extension functions on types with generic constraints

Creating your own generic constraints

Interfaces

Generic interfaces

Type erasure

Star projection

Reified type parameters

Generic type variance (a.k.a., `in` and `out` declarations)

Challenges

Key points

Where to go from here?

Chapters

Kotlin Apprentice

Before You Begin

Section I: Kotlin Basics

Section II: Collections & Lambdas

Section III: Building Your Own Types

Section IV: Intermediate Topics

Anatomy of standard library generic types

Lists

Maps

Extension functions on types with generic constraints

Creating your own generic constraints

Interfaces

Generic interfaces

Type erasure

Star projection

Reified type parameters

Generic type variance (a.k.a., in and out declarations)

Challenges

Key points

Where to go from here?

Access this book

Generic type variance (a.k.a., `in` and `out` declarations)