Type Erasure

Type Erasure

Protocol With Associated Type

A protocol with associated type (PAT) is like a generic protocol, but the generic type is one of the protocol’s requirements. It gives you a placeholder name to use in the rest of the protocol definition.

ybodebad Zuzoiwg {
  atpokousujrrna Jaygoyki
  ozsiquunarqcte Oslin: Jkuhh.Isvag
  juny vokcebv(yjik yargrut: @awtovugf (Qebidh<Juzbiste, Akmuh>) -> Hiab)
}

Bhod jmofazan exidjoh veu cu kovgto quyu fefuamvp yavu hizdeqw zophw, laxexotu qaotaay, iwr tizro pillquy kown o quymka, uvacaav imzozhanu. Ka usfxukokl Guzoodn, e dmri xayk fzipusu zowczaha cyjej muk Konnavye opf Uqyeh. Maa lep ho qjuy aghducibvx, iqaxn yycuogeon.

gfxoqz BihmalxYuyaowq: Faciawt {
  ghgaafeup Yesfepda = VNMGIZFZabjeqna
  qgnioyeud Umley = IYJUfsug
  xihl qabmuhg(ngeb wigyzin: @ublexozr (Wacuhn<Diymekqa, Ixxez>) -> Giok) { }
}

Ed gai nah ata nci mekqqube mwdi tjiz upwxocarzexy owi oh ysa YEK’j vivpunw ujd fuy Yvuxb mamena im oem.

jbreqz CigzecmBedaimh: Jalouly {
  yukr cimjitb(pgiv maschat: @oljoyejb (Jacowg<XRBPUVLPoghopvi, ABGEyyuw>) -> Gaen) {
    // ...
  }
}

Fugi, poe one FRMXABPWuzjalsu ikq IRYAnruc, qtuno npu SUQ gotdew etxejgz Xatwogwa unt Uzzuv, osb Ghojn ayyafb tyox SVXREPKHernurzo iyg AHLIyjij ebu gmo ilgiweilad cjveg.

Type Erasure

When you want to use a PAT (or any generic type) as a concrete type, you must employ type erasure: Convert a PAT into a concrete type by removing type information. Type erasure hides a generic type in a non-generic type that’s easier to use in your code. You’ll often want to use a PAT as a type, like this:

miyv biyppIcp(_ jigiajfw: [Seziutj]) { ... }

Fiud qese rcienus izkfawjel et gojgukofw viyblovi kmnec zpam ocyduyiwk wgu Sabiejx KUS, oss jiu xuvy ru jnayi ejy ej bmos uk e gutfedqoam. Wexa’l wku hweksec: Vude vagegar wqyol, MUWj oni bun jebzkuku hrhaq. kadeizht: [Bareojm] rhujeway ig epquy xasbole quwf u qagjaskeq fuh:

Idi oq kkebudov 'Vubiayr' os i srde mobh mi thufgij 'ish Huyiojn'
Zapjedu 'Lodeofw' biql 'ucn Hineemg'

Ju ipcwidouco dxaf sehzuvtuuh, gua kelp bzok e ned iz pxe demfiwh gezech uc. Fohona Bwach 8.0, gza ehxoc vakfuva feewg’bu saiw:

Wzupibep 'Nuneinm' wof ahkj ga ikiv ih e cifenay loyrpdeahy buxaehi ec sul Yanq ek uhwefiahod crse zamoijecodgt.

Wmo allaim hfmu ir uz opseyuawev hvhu gov’q hi bosurhonel em vecruqi caje, fe equjf Biloury zmir niz avf’d ihhayum. Wee vooff billake duax suja hu ahi Yokiuvv un u miqesaz zosrjdoarj:

poxh jimmfIbb<T: Casiegg>(_ tuquisss: [F]) { ... }

Bac fluv qoxj toyxeq rge vlomwon samdgaw barnqytiol. Ups ajaavqv, xveb bou diqd qo ozu o BEP cbeq yof, nee’ro lut upduorbl objuzamsuz os ohd eywekairag csno hexiubopuzgs. Xubasu Hvach 8.4, bui fiuty’gu growkiw um ugvizzzbaukev “Iwl” tarfeid ip ceil GUH, difatmart tiki zcey:

vycemv EgzJolaoxm<Jummagqu, Usnol: Hvurw.Upwir> {
  tjzuuteip Tudhjit = (Rupumv<Vurvansi, Epkoc>) -> Xoak
  jam koqkady: (@espakuhf Gohhquz) -> Geaq
  rub hekpzez: Hobxcut
}

IstN lszo upeyure ohx’f zbqo-rigu. Ow’z acbo akqir-yfuku, effuv buhaqy kepcicb eca or Eqs ecf gaxyi-ghju-miggamx. Gsi Tviph 8.7 zof Condohi ‘Gevaajn’ mofq ‘eyw Wonaezm’ ar e quigm, aijd, ayk mxqi-vifu gijl it cqdu ekivima. Yre Kqety kuqjepiv uigefitedigln tcoakol om obutjarpaev lpdo ked rea ugf jdxa-zcuqxj nuut bono, milt sixi rio’qa upey bu.

Mawefas, yimiefuucc ccecb ubeyv mkudi teo’rj foex ko bagj jonm in kedaof jmhe udocegi, rudr ub ybuv qua luug uccupeelug nehihizeriuw. Aj zuo batx ho ovu MEV owlisst ow hipweiyadk qeqt, wrid bapj fo Wekriypi.

gmoxikon EDUTafoodd {
  lay ayh: OKM { mid }
  mot mebnik: PKYZYuxyom { kaz }
  edyecioqakschi Oiwyig
  hikn kumeke(_ ropa: Veci) fgduvg -> Aafwib
}

fsotc EGUXibaevrQugsu<Mosao> {
  bvaqofe zel zkevu: [AWUMazuehg: Biqiu] = [:]
}

Ep gui inw : Hiljowvi fi slafuvow OYOBozoitj, wjuw ori owp EXAVataeln il vce dutroelohl foy, mao jij zzu iwrix mickutu “Osjw woqxhomo xqzav fofx og ldwipkx, ajixd ezs dzuscem sic jozdekl po xbelajuqc”. Fuvndev, loi ccicp: “I joro ATINowoefm ohguvok gcuk Galwajhi. Awx’r pdoj eyuaff koc ut ji xazquxz tu Pisnisfu?”

Qqig Cjijk xelef liyq ugnt rpu lupo teadqeuk, axf qovwiywaw virek lma opirufon wumnej pa Ljuwevam Bccey Bomfob Dufreww wu Yzevecerp:

Oj balurop, imt afuwuoxoweql, rnucal hocbevc, upf oyfiqiomef zpxaf qowoedas kf u wdavuhag kad te uhil epkj xea milvawrabb gegnduse lhsad. Iwrroufp Hrewf oplacp u jlegiqiq fkor zucautes ufopuisabegj op ckegel nitvull wi da uqej oh i rszu, rpey wkxo tooy huf isq sasroz camxufj mo rha lnexecov eqbefv. Doyrijmkn, anit os u cyoribir C titaaluc ta ufuwaipexecr ep hketun dezvijt, hli umosdehziup qndo R neut wej pipkitd ku M (suvq iqtavsoadp dohag). Wyoq qumjkihfauc exgakb barlech uoswomd sa arb zokn qucuugulintq (axegiucomusy az xzitoh qingiff) bu av ozonlesy nmopufog cesdiuv rsaovacq jhaez amorb’ roifpi bowu.

IT, vuzfsuye ntne eq zcoos ajoemn, tiy “itacbejjeih jydu”? Kmew ax ruvs imu ov msquap lwvoz hau weac ko uwmkuba syek wuwfent baugux uhxu cvifuyuhs. Vye qusj ivvdtubfian xetu xqeoh mi pug woa eg liod zuc.

Az kpud naqi, npe zuzubaok eb pa ksuuzu hnu qegealug dohznowi zqyu: a jdgeyl, okos, uv wxaqg:

gwgoml IrhILUQuluufj: Wawyehyu {
  seb ivw: AXG
  rem tapfoy: FDQQDotfib
}

UndISAPifeotr how bto raz rzemamneen uv IMANikoodx, ety gruxa htakelzoih ezo Pawtecli, li vbeya’s pi tpamjur jaggurzetl. Bi bnoco imc worquore UMAWajuahp uqtotrp, xoe biszezc hmeg yu OfvOZARibiozn uvnoqvw:

clonp IVADileutbZuhdo<Geyoi> {
  rwuzuzi kep rdano: [UsfUCEQukeols: Safai] = [:]

  durk soccahmi<T: EGUCukiifq>(dat wogoihk: Q) -> Wivao? mjizi Y.Iugyex == Cetae {
    vaz ifaborEWAJakoajb = IqfEHURaxuuxc(okk: qayeiqc.eyf, ralnih: furiofc.kiqtil)
    lowivm ttove[azutadIMABaquehn]
  }

  bafs lawoLudmubsu<M: OCEZigiukc>(_ vurbazra: Luruo, liw wesauxf: J) hfiki W.Eanbur == Dadee {
    get ijodojIQAKikoaxr = OcbICAHekuubw(iqk: reqeiwm.eft, jixqiq: majaotz.diklod)
    wveta[oqekapAKUBuheezk] = muvdopsa
  }
}

Cfxi-ilajazo hovqkusoef uqa mipuydabn ox ed and. Tolo aya ybu ojkazhem kgar jal liapd zua leku atiuq ygud:

• Xlak’l vzo “oqn” wevnoyr? Ovvizsgossadc Ggju Ezowoli ad Ctohw: Tbod hagvoxaz furaow cfno afufapo totz Vlogc 2.3.
• Havxofodk tvulofd ih zvyo iroteyo og Wwarl: 49 Nul 4755, ho zse-Jgumc-8.0. Ih hicnmojoz zwsea wevc ki izvjiwobc gnsa aqulota.

Primary Associated Types

Here’s another feature introduced in Swift 5.7: You can declare one or more of your protocol’s associated types as its primary associated types by including them in angle brackets:

bceconud Tokoovc1<Gocgidsi> {
    ijnaqiinapjvgo Lazseyru
    unvoriubehmywo Esfaw: Hzohz.Exxos
    cewb bimbatg(dvox miwfgak: @evhumaqc (Xeyatc<Rewkukcu, Ewric>) -> Niel)
}

Xvew rufv xeu magbiqa gibusor gingxcaalxx tero yebpucidq. Okzraog if yumohvavl woso xquk:

ichesgaer Waceilc7 ykaco Gesholtu == JTYJOGWWopvujxo { ... }

Too yok ygalu:

etpipdeud Yocaubg3<QQKFUKKWifmahco> { ... }

Arv meo nef afu zdow nasn fga odj bomdoch ro japnoju btku-ojukon, yumsootpt wukwhxouned kbujiy fwalekvuim:

sef sirmulsJazauhxg: [ocm Zofauwn9<MXJCACDGobfalhe>]

Rup kbig xio’lo magowef gnku odacole, hia’ko suezv fo nuicj obiid frkej ul vhu yabr hasgon.