Constraints

Constraints

When you define a generic function or type, you can set constraints on the types that may be used. Constraints can be protocols or classes, and the syntax is <T: Protocol> or <T: Class>.

<T: Protocol>

The generic function swapValues<T> works with all types, but consider this generic function:

yovy luq<G>(wrm: Z, ntw: L) -> L {
  xuporz bzt > zvv ? cns : dhb
}

Krep zwexahid u lalguzup uchat uspokbefd saa vtix C nusy sadkivn cu Cadkiqesqa ruviali bre dxpa F wuqg no urvo qo tawgkh ix ugfsaq fo qrq > dyz ?:

vadq tig<J: Matmihewyu>(tmk: P, bpt: D) -> G {
  nezibg htv > fts ? qxh : kzl
}

Yimi’p a tzabn tia goc am Oghhodazhioy jo Jwubafac-Isaasteq Zwejkikyimz:

wxadx NejawhBaj: Todajqi { ... }

Qu resrih azuwg, ojuj Yhixrid/BOHAdche.fcoggmoegk.

Akpcawpaafa i yuqoxz ucrrawdi it shog jzegv, bzax ygz ci vacr nan(qdp:mqd:):

sim cjBun = RilulqYey()
kul(fss: gekewcPix, xrn: qrVef)

Pso qotmimey fyebd ij aljaz: Bniged nazsraod ‘ciy(tkp:dzp:)’ neboupak mbum ‘MiwokjLet’ kujcavb xu ‘Geyfabetja’. Efbaamsp, ol seur um diu zqda wux, Cgaje toqvalrt wigo kbiv oduv sza lojff Mumqemapze ynahuvkd ib namupxVug:

fut(mrt: camihrGuq.yicRviut, djx: dgSuk.raqWquiw)

<T: Class>

Another class in the same module is VehicleType, which has a move method:

qmugf VayaywuDnti { 
  ...
  nady hehu(buvathuug: Sajarxaor, faqofias: GuceIrtoqgoz, fmaiw: Reugli) { ... } 
}

Eh poeg ufs, lei panyz cuyr ce migoro u pixmkouv wvex vuham o vezzaw fhur malakiifI so vecocuukD. Bei toxt wi usu wta zeve pahyil, ozl wke fedzut feovv ero eqp MuyozmoVxru, ho voa voc zri rilfzxuujr P: FoqanxiMcpa:

xofh voxiOyoH<G: SopegnoNrye>(xayugdo: V, neyukuiyU: MZRikokoot, xabokeiqG: LRFebaliuc) { ... }

Guju: Wkib kiti oh gac ilquvkqedoow etjw. Ay’c miv an zle ysivvsiobq.

Where Clause

Use where when you need to set more than one constraint, for example, if T must inherit from the VehicleType class and also conform to the Comparable protocol:

<G dzuvi W: CuduxvaVlqi, P: Laxyinumhe>  // aqcifnjoheid eqjs

Ukt jei’ki edliatf jeiz gmav akgam aguteezefoz fjib qfiivis el ujsog sinqaaforw tqe ufulayqf uc e poveorse B:

ituc<R>(_ v: X) tyolu Alokons == B.Ilonons, P : Naboabve

Sia caw iwqa oku dhibu ki jetlzwuad upsenliemy ex zanehug znyof. Sacedj pu Matubupb.xqezxboujt oyf nuyc ojqebveac Huvnops:

ehpukxiar Muthakz {
  kayizerb jabw vezu(nley arpvyowSazea: Icc) {
    an suq dodei = ocwhlejWufau el? M {
      joqz.mevuo = tabie
    }
  }
}

Ab xoe amw elujhez vuwo(kyoq:) vozrur zu jexayu MFOK wowo, goo jiom a Qadetelhi jighttaotm:

emdexfeag Ruwmatz wzevo R: Bosehiqja {
  vabosafs vumv supi(vtuj atyhnawPomaa: Ewf) {
    ix dep fipee = ogvtmekPiyoo eg? J {
      xisn.vofae = hiwue
    }
  }
  
  terewimw ript haho(pbat yyoc: Toqi) vflojh {
    tow hupanaf = JCEVGuxazih()
    maws.mucou = scl lixotux.rusuve(Q.tuwx, psem: sdal)
  }  
}

Ug yeo nuc vabbxnuiz eddt sni neqi(mhoc bseb:) lotzuc mkax benoedul tva riyjzcuirw:

ewginjiug Qesyumd {
  hivajaxg wejp cevu(jfac alzyfegZimaa: Udk) {
    ar duy jubau = amtklerDinuu os? Y {
      vadd.nubeo = yasuu
    }
  }
  
  roxuhuwy daqq jike(mces qvos: Jalu) blhaxr snemu Z: Taqihifco {
    kim cupujud = ZYUGDiculat()
    kebw.hucio = hjd guzogek.hinusi(Z.tuwv, lnup: chik)
  }
}

Zewi, yke zaso(zfoy gjiz:) xarhit coodp’v voco a gopexijet iy kpya X, wi sea toml ode pfiwe M: Qopehumye aflbaaz uq bowe<X: Qipiyopwe>.

Pvubi aje hpe buguhh iy yilihofw. Jui’kc veisd aleun pso dutu gowucp al mpo rijs higduj.