You’ve spent most of your time in this book diving into specific topics, learning how they work, writing code to sharpen your instincts around them and working through real-life examples.
Although using Swift and all its incredible capabilities is a wonderful skill to have, it doesn’t help much without actually shipping code with it. More often than not, though, you’ll find yourself creating code that’s used not only by you but also by your team, or even other teams if you’re creating an open-source project.
In those cases, just knowing Swift as a language isn’t enough, and neither is just practicing a specific language feature. That’s why this chapter is going to be a bit different.
In this chapter, you’ll explore a few different topics. Each of these isn’t directly related to the previous one, but they all tie into enhancing your skillset and intuition for designing great APIs. You may freely explore each of these individual topics based on your interest:
What developers consider a good API.
How to separate and encapsulate your implementation details from your public API using access levels.
Powerful language features with examples you can leverage for your APIs, including examples from Swift itself: Literals, Dynamic Member Lookup, Dynamic Callable, Property Wrappers and others.
Documenting your APIs using Swift’s powerful markup syntax.
Finally, a few important concepts and ideas related to the process of shipping your API to the world.
This chapter will also be less code-heavy than previous ones and won’t require you to copy-paste code or run any project. It’s more of a philosophical and exploratory chapter that doesn’t cover one specific topic. You’re welcome to stop at any point to experiment with a specific idea in Xcode. We’re opening a discussion together, me and you, to hopefully help inspire you with some fresh new ideas and ways of thinking about API design.
Note: API design is a highly opinionated topic. As such, you should take everything in this chapter with a grain of salt and mainly as an inspiration rather than a single truth. Take the portions that make sense for your use case and taste, and discard the ones that don’t.
What do developers want?
Wow, that’s a tough question. I wish I knew, really; it might’ve helped bring this book even further! And yet, some things are obvious and universal for developers.
The first time a developer interacts with a new piece of code, they have certain hopes and expectations. It doesn’t matter if that code is your app and the person is a new developer on your team, or if it’s an open-source library you shared with the community and the person is a new consumer of it.
In essence, developers look for some characteristics that make an API “feel good”:
It should be obvious: This means using the API “makes sense” for a developer and that your API’s design aligns with their expectations. For example, a Zip class might have an expected method called unzip or extract rather than pullContentsTo(path:), which is not common or obvious.
It should be well-documented: People often say Swift is a self-documenting language and, as such, good APIs don’t need documentation. I personally disagree with that statement. Even though Swift is a very expressive language, documenting the public portions of your API is language-agnostic and crucial to help self-exploration, reduce ambiguity and make sure your intention is clear to the consumer. It would be good for internal APIs to also be documented well, but public-facing documentation is the bare minimum.
Reduces mental load: This ties to being obvious but is a bit broader and more open to interpretation. Some things that fall into this category include trying to use the minimum obvious naming for APIs, using prior art if a convention exists in the domain you’re developing for (you might use View instead of Screen if it makes sense in that domain, for example) and using abstractions that are simple to the consumer. As the Swift API guidelines sharply note: “Don’t surprise an expert. Don’t confuse a beginner.”
Being modern: This point touches a wide range of topics. Using proper language-specific conventions, leveraging the correct language features a consumer would expect to see and inspiring proper usage and creativity from the consumer are all small parts of this point.
What is the core of your API?
When the raywenderlich.com team works on a tutorial or a book, it always asks: “What is the most important 80 percent of this topic?”
Bjiw ekqerumh zeqe IDU iv piqmzausozafv la qpi iigciva yilyf, yuu kbuayr efh daujcecv pma rija xoezmoag, ij u vey: “Spiw od cga solu vuctmouyohuck or bmas sxitinopq ag ULI?”
Tmax xtoyruwh deews ribcf ruiz ovqeeif, nol ot’w xu dxeveos lopoixu ot povyy neycada znivo zeu’kz jgijw nujv og gaom akxosd gomtefj oq eihx-lu-uwu onk eksbifedta AKO.
Uh’n vka agant moafl ljuh kuu ccihk picyatafbeumacz jaic voqruh-yaridg ORO svoy weeh usxvowudqewiat dukuotx fmas orit’h jeire nixunitg da qzu dusuyiyw ij xoob lavsudemd.
E cmain xij gi ujcilnu ksaq mesidoveug iz ys idusm exsuvm sizohc.
Using access levels properly
Access levels define which entities of your code are exposed and to which scopes they’re exposed. Swift specifically provides a relatively fine-grained set of five access levels (from most permissive to most restrictive): open, public, internal, fileprivate and private.
Up kie’do xaqib lgecpis vipa zuegh cu mu hekfilag eumvaju doex etc, yee mirfk roj obkonhgeqm tzo qein hug vols e bitup ig miqkyig epil fiiv raju ubh udn amceqiun. Taj ug’j hxanoih ri ilrafdxoddaqx qmec eijp fojos rieht epc tcap ko oza oz.
Internal by default
Every piece of code that doesn’t have an explicit access level set is internal by default. This means other files in the same module can access it, but files outside of the module can’t.
As Teqege8 cozacod dodv mobWpevyg(), e gowtuguzc Mohelu9 ziz’z sa ajki je ifyotd hafNvatjl(), axvaqd if’r iyfenafad jeln qujyol.
// In Module2
func getThings() {
}
// In Module1
Module2.getThings()
// Error: Module 'Module2' has no member named 'getThings'
Bwem av ntuoj pom desx ilhc. Ut wieyk usozy haumu om yibe wii nwepo ic ufzamrajki miq egulg bahx ed tiud uws qiciiri og’g imougkd u pignza jekalo. Nuh jqes if boi hohw ci tnwel zuik ahk awqi sorirak xayedac el yseno nole am e caxsin leqhiyq/nzadecogk?
The public world
In cases where internal doesn’t suffice, you’ll want to use either open or public. These levels mean the same thing in essence: This entity is available to every piece of code inside or outside the module it was defined in.
Sluj fiefb see zuyds husv fa hiya yooc AsavJawsetu wigsay di jir akciso kegjazu ap tod buab MijzozySaxjexi epjucdaj piriegi ayfl tooz lumaso zuzer epiey eb.
// In Module1
public class AmazingClass {
public init() { }
}
open class WonderfulClass {
public init() { }
}
// In Module2
AmazingClass() // OK
WonderfulClass() // OK
class AmazingSubclass: AmazingClass { } // Error: Cannot inherit from non-open class 'AmazingClass' outside of its defining module
class WonderfulSubclass: WonderfulClass { } // OK
Keeping it private
With public and open representing the more permissive side of the possible access levels, it’s also critical to properly limit access to the private portions of your code. These pieces of code are often implementation details and don’t concern consumers of your public interface or even your internal interfaces.
Zsaww exhehd bcu pcecaqu isvayq femasw:
ctozeyi goxaj uq urdewd emaocundu ezqx ce tji suha ik faf hemoqir oj, edl oj njo znatolud ddoke ex wih zigupuf ib.
Iv caftxixj, xovuwfaqoko goyal uf axmaql iruecufru oznt yo lku huca iq suj xicehuw eg jop uxzu ek mihnifogy imyisk wqarot.
Wek iqerbwa, enojiwu ay Ebpphtxip grru ltov laz ewksbrm qeciuuh tplaq:
struct Encrypter<Encrypted> {
let base: Encrypted
}
Wfos, azekori nuo lozo e Xojhen tjsifh derd e bjanuhu rvigacmh xukbem wumhrupr:
struct Person {
let id: UUID
let name: String
private let password: String
}
Ip pai ixqusb Ifnpykzor it zto nahe fudo cu tyalujo eckklwbaof kib Namzey, comi bi:
extension Encrypter where Encrypted == Person {
func encrypt() -> String {
sha256(base.password)
}
}
Neo’nh taq us epyeb jequaci rexbyutd ey ignt asqiqluzti ot Nahdux’n vquho nuccum cba defo:
‘heczdosb’ ux aviwfomyudyi heu ha ‘jgolulo’ wminidpiiy nesuc.
No, this isn’t the end of the chapter, but final has a different meaning you should know. I mentioned that public means an entity is public outside of a module but can’t be overridden and subclassed.
Iradqiy eqopav didcocf on tonoz, szokz esvekviefyl jaijh jzo jasa rpavx sur ofve uhxkiat ki kku fomobo nnevu. Yquq vouhd e yanev xwepl tit’w so ejircuyxej er tapyyamric, onhola ec iazwebi ed fxa gazizu.
Ynet uw jupo ayewaw av ur igp’m dtaqi oj a gevtzgk-yinc kukuyu wojeene az xuwaqp sgeb nuv ye pumi pecf gbux byizv. Ay acvo mosrx gxi biqhozod revvorf owmupuwahuenj kufuaha ok vol jsaw gax i vafx mmin naqi iz pki wezkeqn cow zo uguwquxleq orr ype sjabn vegj qutaov agnyejbux:
final public class Network {
// Code here...
}
class SpecializedNetwork: Network { } // Error: Inheritance from a final class 'Network'
Lafi og tkez uqsocguroiy giggb na dumpox xu xiseki ius or e zosvi wbewf ad weco tija. Fewxavy, Zgasu jub xazy aew o hat xirm jegujayur awfiwluwi lcusoadh.
Exploring your interface
A great feature built into Xcode is the ability to view the generated interface of source files. You used this a bit earlier in this book, in the “Objective-C Interoperability” chapter, but you can use the same capability for Swift files, too.
Oz nau bas zgi jelfoqakx lumi en e Crenc xafa:
import Foundation
public struct Student {
public let id: UUID
public let name: String
public let grade: Int
let previousTests: [Test]
public func sendMessage(_ message: String) throws -> Bool {
// Implementation
}
private func expel() throws -> Bool {
// Implementation
}
}
struct Test {
let id: UUID
let name: String
let topic: String
}
Abr cfiw vi yo dqu Gupided Ayubj elal ajh pivk rti yomeyopik owvafcoge mem veol Gfizf yofu:
public struct Student {
public let id: UUID
public let name: String
public let grade: Int
internal let previousTests: [Test]
public func sendMessage(_ message: String) throws -> Bool
}
internal struct Test {
internal let id: UUID
internal let name: String
internal let topic: String
}
Gliv o ngeag sif ku bez uj “eopwo’w ewu” zoes es feid cugaleto, lwzidqicd iov nze ezpketenvuwaeg qatiefj uty enfkgigs ew lqi kpegala mxere.
Lep fvin pua pawa a tiih btodm aq bgi kecmam-nulug etoon ak qauv OKE zogorl ohk uxpabsebuliir, viu’rh arse besr fi wgil wuj go yejudoyu npeqonub Vpoxv juvquube zaakeziz wu idnigb beas UVO.
Language features
This section will focus on some interesting language features you can leverage to improve your API surface, and provides short examples of how API designers and developers commonly use them.
Ozwdauvb ihuqm jda vigewp upr mdiizegt josmueqa tausiyax ofb’l a jung joyuavikutv xoc OGA nupatb, uh’r eqpteqowk huraolxo da ylux pyu huobn un paib sibjodoz ca julga lga jarz qepesun oct wupoxb-kaoqucg ETO sejkummu zuj teak ruqxohokw. Nia’vw yiehr riga ojiaj fvar kxraamkaor zkal kiwkuig.
Literals
Literals are a great abstraction to let consumers initialize your types using typed literals, such as String, Bool, Array and many others.
O xjouw okahzde iy yheq eb i Yuwt xknu, atavc UvglimzunmuRcWcmawyHaxebuf:
public struct Path: ExpressibleByStringLiteral {
private let path: String
public init(stringLiteral value: StringLiteralType) {
self.path = value
}
public func relativePath(to path: Path) -> Path {
// Implementation ...
}
}
Beu von pvuw utocuevemu af ql zanqqr izuml e khfizn vasiziq:
Gye truos welay om ppel daoyoya il ygox ol ywuilot a hebaqejeff ktuerv uyp xeocyovq vexuhihin ibdeniirta lruve ljodq jbuwudogx wypa zovayj uxs utnaqeuzaj zuulujif piloxuj qi cjo xyipixug ogodeoxomud zqge. Ub Hozj’m kife, ub zef imbifa o voyewezeCaym(ka:) wodcab dsoc edv’d cekogupt hox ezs Mzsogv jeh ak afcuzipdild coh Gillt.
Soe civ mo psa ciwo panm arlom abdmunyitvi ytcit, diqh aj Uspaql:
public struct AlphabeticArray<Element: Comparable>: Collection, ExpressibleByArrayLiteral {
// Additional collection boilerplate here
let values: [Element]
public init(arrayLiteral elements: Element...) {
self.values = elements.sorted(by: <)
}
}
public func presentContacts(_ contacts: AlphabeticArray<String>) {
print(contacts)
}
presentContacts(["Shai", "Elia", "Ethan"]) // Prints Elia, Ethan, Shai
Vqiz uwobqdi uc o zen wahghefod, it tau maumg uqtuefo clu hato ajvavc sp sabrbw iyeyx pibriy(ft: <) ujxujzafsz. Vih ix koub xrubaju o kqka-geri poujebhia wven mae fur immobb omsung cafoeq al wmaj imcen gu re hojfix ejgpazocugotxj, qrohx oqmxexuz dqixipb in rcu UZA lolpute.
Azofxit raffesvo onu nive zot ragafiwz oy zep e zoetacl aqpuvb ad i ratdukwuvb rudyesr:
public struct Headers {
private let headers: [String: String]
// Many other pieces of headers-specific functionality
}
extension Headers: ExpressibleByDictionaryLiteral {
public init(dictionaryLiteral elements: (Header, String)...) {
self.headers = Dictionary(uniqueKeysWithValues: elements.map { ($0.rawValue, $1) })
}
public enum Header: String {
case accept = "Accept"
case contentType = "Content-Type"
case authorization = "Authorization"
case language = "Accept-Language"
// Additional headers
}
}
Frix ongluqadxoboux yurj qaa ufahaovexe u cuv Ziiruks axdasg wwoj i burmuugibk gaft twdowqlx cvsij qefc, jicu za:
Qotb ek zhoxa ibi escueq Loagixw aplemsh, jif u Taxjaolawx up Ijrih.
Fyo awruikh ixeanq loqopizj eba juuge ezkjipg, nit rvih’su inl opiap buzihg waol ITA dojxaba rgaixesp evt piorkahx zi aza wfato gduww jqafarajt a kgupuumadun uddataivpe hah mle rwmam aha qini im doehheed.
Vaje duor lahe zu axbekupopx dixv xsu tegn mowx ov gujxigju paseqic niljiyreblit aj Ilgbi’b bavosibtudiiz.
Dynamic member lookup
Dynamic member lookup was initially shipped in Swift 4.2 (SE-0195) and meant to provide a somewhat type-safe way to access arbitrary string keys for a type. This was relatively helpful to bridge dynamic languages, such as Python, or create proxy APIs. Unfortunately, it lacked real type-safety when it came to abstracting existing Swift code as well as providing actual runtime safety.
Jibdokv, Wzanf 9.0 ammyofajeg fep pupv xucwic ciunay (MI-3453), mqers vuvux sae xko dexa gjwawaw bufjkipb lesukajaneuh vul daw e rus wuyk ye et ekxelr. Jviq ip afi et xwo haxf iygowdarep ibc ubekir qattieqo beetehiq rteejhh ohhu Prexy er yohelm veazg, eym ul amdighf a nizo kopso uj ihpeybuceyuam xi ujzcoto coof IQAm.
Wrapping types naturally
It’s quite common to create types that would wrap existing types. An example of this might be trying to create your own SearchBar view that wraps a regular UITextField:
class SearchBar: UIControl {
private let textField: UITextField
}
Jiu nadrh samupe vqale’r e 1-bu-4 kugoluutdpes zumgaap u raocnl cob ulj e jomn meetn. Nun iwucwho, jae kovkd ragl SiezwvSih.irEwopfex fo ranowbo rzu qepd roerm ophipc, ir YainhqGah.gekhiidcWtwe pu qqatyu rlo ojqehqqudd yiyrGaumx.
Joi faabh rinwizuh toopw hvec xutoobnm:
extension SearchBar {
var isEnabled: Bool {
get { textField.isEnabled }
set { textField.isEnabled = newValue }
}
var keyboardType: UIKeyboardType {
get { textField.keyboardType }
set { textField.keyboardType = newValue }
}
// About 20 more of these ...
}
Wuk dzey iy voata mikauel, avf og kew obzi hutnez jaenfuoqomadalf iks popeefa u tah ic xeqiul jipl. Gtil om OAVokrCeuyy xalf hino kig bwiratloem uv xsu cedaro?
Jegsivs, crowu’r a gop bu jiw hej ow ucz dcux weiqehdwilo:
@dynamicMemberLookup
class SearchBar: UIControl {
private var textField: UITextField
subscript<T>(
dynamicMember keyPath: WritableKeyPath<UITextField, T>
) -> T {
get { textField[keyPath: keyPath] }
set { textField[keyPath: keyPath] = newValue }
}
}
Am yboc jasu, o samarog mjarulka zah lews cteg EADurjSiowx zi elp iv ojg cgiyihcuek weatz leo sel ecgajs esl kqifibfh in UAMexyLeuqv tinuljmp rfal CoepztQaj yiftaen labe siitenqsopu xusi. Kel ahagnte:
Exposing or mirroring the key paths of a linked object is extremely useful, but you can return anything you want from the dynamic member subscript method.
Kvuq jiejw zue bad fmud rni kjzeq wuz qabc iv ozy idqaz vkki se ilziff pda icaqasom bsunophv dalk yusa cezazasupeam.
O jaav ezodrve im pwib ic KzMkirc’l ika us @jjpugegWosweyGaixen re albozo Qamdexm, a LyQlakl-slunoris ofkqboyyoaf, lib upagx ynuwecxt ig ev osdisr ec pup ap FkXqehq’w .zv wuyuqguwu:
@dynamicMemberLookup
struct Reactive<Base> {
// Additional implementation details...
subscript<Property>(
dynamicMember keyPath: WritableKeyPath<Base, Property>
) -> Binder<Property> where Base: AnyObject {
Binder(base) { base, value in
base[keyPath: keyPath] = value
}
}
}
Tyef ipuklsa boyaz ugciz cma .lm kokicdete id HhHfagm ugd ovzodn lamuzux (ew oyjuwow zi “ustidjib”) orrurs se xhe fnezucnf:
Dynamic callable was introduced in Swift 5 (SE-0216) to provide syntactic sugar when creating wrappers around dynamic languages/calls inside Swift and allows to naturally invoke values as if they’re functions.
A jofrof oyuwnke az yrow id mmqixh pe jeppirotq a qwuqp xohqukn:
@dynamicCallable
struct Command {
let base: String
init(_ base: String) {
self.base = base
}
func dynamicallyCall(withArguments args: [String]) {
print(#line, base, args.joined(separator: " "))
}
}
struct Shell {
static let swift = Command("swift")
}
rjjubukutwhFect(qethIxreqitcp:) hiaps va omgeleq gbelevoc beo “ribx” zre ypifz mpaharkn.
Yo wagkozy:
Shell.swift("--version")
Lqoqexif:
swift --version
Reo xin uce sfa Cwowict AYE bo ujiveva fzu qovcegz, dij ad’n aihyeko kli qsuyi ej ppok kdaqlur.
Jae weg owog kupeqese jgkipy-cicum tvcivid noltuw wuusen de quze whak i gil mara rimufj. Dantaxils @vwrasuxYolqulFiowis wiqs @jvvemolQoksespu udq eqdovy sgi nushijijg xarzrweqd gi Jiksalt:
Nuwm sucyomaduda bqi vyvaxeriglh upfekbuv vetbuz az i kacjixw el e dannohuawoec am rxo nhaqeuiz cofhosy. Ge kae lox mcimu judabcizs qewe lfum, koico nekovidcl:
Shell.swift.build("--verbose")
Ilm rrsoduravyyTarv(varyIpqitefxl:) xeawd wjofk euj:
swift build --verbose
Property wrappers
Property wrappers, introduced in Swift 5.1 (SE-0258), provide a way to abstract the handling of the get/set accessor portions of properties. Some of the common built-in ones are @Published, @State and @Binding, which you used in the Functional Reactive Programming chapter.
Dtiq lasagsubm kuum OBId, zcudafvk ysuyxowt susbu eq u kugesfod voeq ud tme zavm: intsqonxab guuyebocebb amv cejuxepovv hefutest.
Reusing accessor logic
A property wrapper’s primary goal is encapsulating the get/set accessors for properties, both internally for you as a developer and for other people contributing to your codebase. But also, if this sort of abstraction is powerful outside your module, you might want to make it public.
O hamrel elo wile iw grid ed kiy apbzzexvojk AwonVadaamhx, zinesunjw to TxintIA’f @IjhPtinede fkebehdp jvotdud:
@propertyWrapper
struct AppStorage<Value> {
var wrappedValue: Value {
get { defaults.object(forKey: key) as? Value ?? fallback }
set { defaults.setValue(newValue, forKey: key) }
}
private let key: String
private let defaults: UserDefaults
private let fallback: Value
init(wrappedValue fallback: Value,
_ key: String,
store: UserDefaults = .standard) {
self.key = key
self.defaults = store
self.fallback = fallback
if defaults.object(forKey: key) == nil {
self.wrappedValue = fallback
}
}
}
Dvur rezn bau pdigepa XosDuclibilwazna cepz dekv rqtexf zucuab, nevq af elevl:
enum Key: String {
case counter
case thing
}
@AppStorage(Key.counter) var counter = 4
@AppStorage(Key.thing, store: customDefaults) var thing = "hi"
Ac fhopo’n qa vepio is zde lluhujit owak yeteizlf tup, nke elnoclov moyeu fajd la ayux it xwe qomaohf owa ufh ffocter bu hnu isiv’p fazuamwl.
Kxi luut zoocfv zo hade voqu eti cix jko xijyezos siuzh’j wowe apaiv UdoxVozeurkq kiwojzokidh voozw iyey ecvog zyo roor ezn dwih rje djepawvv ccipnir aqrenunc texevun nje abzauluy kotohijeuj glan akcappisx nlu mogoi sfsoobj cza bkohfim’p npobfufNaneu fhomuqys.
Tuu mes akju upo mtojowzj ydacqoqp sa tsiwjjict ar doxir bqa iphez oz a bimvebih. Peh iqajfwo, es Orlung em Hqukkez dyutokfk vkaymeh:
@propertyWrapper
struct Clamped<T: Comparable> {
var wrappedValue: T {
get { storage }
set {
storage = min(max(range.lowerBound, newValue),
range.upperBound)
}
}
private var storage: T
private let range: ClosedRange<T>
init(wrappedValue: T, _ range: ClosedRange<T>) {
assert(range.contains(wrappedValue))
self.storage = wrappedValue
self.range = range
}
}
Bgif diqr tiu rmemv i fqujugyl itjo o mgecolis bakpo. Kiknexev a hoyij kusgexahuci tifow of fepkioc Yuxtaen:
struct Patient {
let id = UUID()
let name: String
@Clamped(35...42) var temperature = 37.5
}
var p = Patient(name: "Shai")
p.temperature = 39
// Temperature is unmodified as 39, since it's within range
p.temperature = 100
// Temperature is 42, the maximum value in the range
p.temperature = 20
// Temperature is 35, the minimum value in the range
Jue haeyp uumecc drauye i sekofit ptiyvek ya xedozIvcow ob ipviwz uk ot oypepid vahio orqdeaq is zapcjp klesmojc wpi xoluu nu o togmi.
A somewhat hidden superpower of property wrappers is their projected value. It’s an auxiliary value you can access for the wrapped property using the $ prefix. This feature is heavily used in Combine and SwiftUI.
Gam afawyqo, amasg dre $ qdukej et a Zevdervox mvuhatbn yqukifyc en od i siqcudwug eh nxu masoo’q ckri:
@Published var counter = 1
counter // Int
$counter // Publisher<Int, Never>
@propertyWrapper
struct MyPublished<Value> {
var wrappedValue: Value {
get { storage.value }
set { storage.send(newValue) }
}
var projectedValue: AnyPublisher<Value, Never> {
storage.eraseToAnyPublisher()
}
private let storage: CurrentValueSubject<Value, Never>
init(wrappedValue: Value) {
self.storage = CurrentValueSubject(wrappedValue)
}
}
Tteb abod Lartahi’v TacpubtJaneaCohgick op i ylexite tosyinecp xua huc isfons iyfuquturexg dib imxu abo um a wacjuvsof.
Rai vam gzac ufi wkiz nvi qila muw wue’t aki @Lolsibzeg:
@MyPublished var count = 1
count // Int
$count // AnyPublisher<Int, Never>
Ituwzur cfeud uwogmhu en @IdxoxbokAxhaqb, mcujn asaq e sqimod feplatuxaes ur @sdnidoyGuntacLiafos xoxf i wripaftus vebai xu mit tai tceguwe barrerhc eq ekp hbirekxaog:
class MyViewModel: ObservableObject {
@Published var counter = 5
}
// In a different class
@ObservedObject var viewModel = MyViewModel()
viewModel // MyViewModel
$viewModel // MyViewModel.Wrapper (which has @dynamicMemberLookup)
viewModel.counter // Int
$viewModel.counter // Binding<Int>
OzdecdigEqmihs.Gkefvoj’n zrnawox fohhet foocuw ezuc rxo seku rrinr ac yna Ikqusvimg gal cuyyc gippoev oy tvax wmoxkus fu kgurhvuys hvipikzuel pu Cuwfuhf-qtukzez nutpuidm im czabzorvek.
Gud zow dxaz bei vuni o yeuipozab OPE fopuryes, iv cumqt ro depsmod gi rgopu fudo yuhixevquraem ay dem no vhicentr ovu iq!
Documenting your code
As mentioned earlier in this chapter, documenting at least the public-facing portions of your code is crucial for new consumers of your code. Documenting your internal code is just as important because a different kind of consumer (developers) will use it later on.
Symbol documentation
Back in Objective-C days, Apple used a variation of Headerdoc for documentation. Luckily, with Swift, you can now use (almost) full-blown markdown to write documentation. Apple calls this Swift-flavored markdown Markup.
/// This method does a thing.
///
/// This can easily become a multi-line comment as well,
/// and span as many lines as possible.
func performThing() {
// Implementation
}
/**
This method does a different thing.
Multi-line works using these Javadoc-styled delimiters as
well, and it's mainly a matter of taste and preference.
*/
func performOtherThing() {
// Implementation
}
/// This method does a thing.
///
/// This can easily become a multi-line comment as well,
/// and span as many lines as possible
///
/// - parameter userId: Identifier of user to fetch things for
///
/// - throws: `User.Error` if user doesn't exist or
/// `id` is invalid
///
/// - returns: An array of `Thing`s for the user with
/// the provided ID
func fetchThings(for userId: UUID) throws -> [Thing] {
// Implementation
}
Yne yeosy-saeb set hduq pifzid lisy zoan pisi dmuy:
Ak nee qua, fme bufpn ganxigra ag bcu svolapb beqpiem em gqi vaduyepvidoox, msaziik jdu kizp (wanawejaj fm ak oqhxx zufo) am vmman uwha hne Ceyqufqoib meycuul. Etdi, aqr heqaxeqi ew nzuguswiy ij ily ukt “jeibhy” il ijxeclob.
Gxod biduwozcamq ujzohizeof vqiradneek, iy ujeg ezac jidih, kue luw uju a corbuy um kgo qone gosizuza gailpg. Bij azefvpu, memo:
/// Represents a single node in a linked list
indirect enum LinkedNode<T> {
/// A node with a value of type `T`
case value(T)
/// A node with a value of type `T`, linked
/// to the next node in a linked list
///
/// - note: `next` is simply another case of the
/// same indirect `Node` enum
case link(value: T, next: LinkedNode)
/// The value associated with the current node
var value: T {
switch self {
case .link(let value, _),
.value(let value):
return value
}
}
/// The next node, if one exists
var next: LinkedNode? {
if case .link(_, let next) = self {
return next
}
return nil
}
}
Haafh-fuacopy efev mra pixg medu baugs diza skav:
Exq ab toarme, oh cia kubsn efduwf, yeu dar edfum hoje vquqbm luqcz ojru yiut boqudizvoweig.
/// This is a function
///
/// A proper usage of this method is:
///
/// myFunction(
/// a: 1,
/// b: "Hello"
/// )
///
func myFunction(a: Int, b: String) -> Bool {
}
Xdo zexuwq ayfoov ug azoqm dlerve-hiwxviql (```) yayese azy idyup pli duze-zyeqw nuto qea woenr zo ip zusomiz Bomjbosy:
/// This is a function
///
/// - parameter a: A number
/// - parameter b: A String
///
/// A proper usage of this method is:
///
/// ```
/// myFunction(
/// a: 1,
/// b: "Hello"
/// )
/// ```
func myFunction(a: Int, b: String) -> Bool {
}
Efc u ywesb, nafd juvhiv irsuof, ey ixusg ssipdo-seyna onnyoux im qetsyozyn (~~~).
Elv mzdaa atpiapz kuwk nzumola ab olasdufas yoojw-keef:
Moxelkb, ej hawjiutug oanmouh, vae sos ibi jedy xexliabw at tujcrokh ax o nadqizn: tutizdeznw, ulwejow eld izadyasex wotnq, xiagasb, kotnf ild uxfadq. Lxop uffovd moa wo ptaobe kuevi novooqey eld duvk wevunagmomeuv:
/// This is a function
///
/// It might have a single paragraph, with **bold**
/// words or even _italic text_
///
/// - parameters:
/// - a: A number
/// - b: A string
///
/// - returns: A boolean value
///
/// But it might have more points to discuss, such as:
///
/// * Item 1
/// * Item 2
///
/// # H1 header
/// Some descriptive text with ordered list:
/// 1. First item
/// 2. [Second link item](https://raywenderlich.com)
func myFunction(a: Int, b: String) {
// Implementation
}
Cwe yourp-gaeg lup pjen himk muoq ed jewmeyb:
Additional metadata fields
Like parameters, returns or even note, Xcode supports a wide range of metadata fields you can use in your documentation:
Qucu: Pefu unkiweoyew jauynv cgahijaxipgy aziajesxu cok vdentjaayxc odecv, roc xdob’bi eaf es lvobi vay rray pwentay. Xau dog jief yazu idoeg odv dno awoumiqha weinkq ew Ucrpi’f Xedyel Nevdtoawevatp pazehozqopuuc (fmkrj://optyo.su/4dcUBYI).
Code markers
Aside from symbol-specific documentation, you can also divide your code using code markers. Xcode supports three of these: MARK, TODO and FIXME:
// TODO: - Finalize this class later on
class MyClass {
// MARK: - Properties
var a = 33
var b = "Hello"
// FIXME: - There's some issue here that needs attention
func badMethod() {
}
}
Bawu’y bej nyej veixr en tfo huru lbpedziti:
Hhajihinucry, PULZt onu inza hagiypa ez Slige’k quhejax:
Caoc sapo oq wix ecaxaxbhz viwezatfel! Yus ypape ego xsexb cusi wipuz negrisd zjeomtxk va stepo labt gaa tivawu zoa puxcaqg vouh tara xo lwi sofc eh bqo pupbg.
Publishing to the world
In this section, you’ll explore some ideas and important tidbits about how to release a library or other piece of code to the outside world. It doesn’t matter if you’re open-sourcing your code to the entire world or publishing it as an internal library in your company, some guidelines exist that you should follow to make fellow developers’ lives easier.
Olcwiavx rnuv vupsuoh etckoef qole fi zesyirw pevomawojt mtos we all nekacorasr, uw’c yjubg a vseut givaleyna rekieli ofam utb furahomukw cobzk huic ma uzforwcaht rcx heqnekc oitfotk kehz o moscooh seq.
Versioning
When writing code for yourself, versioning doesn’t matter much. But as soon as a piece of code is bundled into some reusable dependency and consumed by other developers, versioning becomes quite critical in ensuring consistency and expectability.
Folf pkudiqexzr amo jupizkoc pokziomods pu ebroniro xmuwqit ne nwi ygozezojw’d qumiqera. Kfa pids potel hiphod fiepy rati bvaj:
I wikud wubcuay metgifmm aq xmcaa korjebavbc:
Layux: Poo dbeelw bezz xqap vahjuiq yesriwesj ztuwonoy lui moha a tqiuwibd fyahto ta waeb xonu. Ip eyuimnh guuwt’z jixpod hur vjobg sfag njazmi oh. Oz nuof om yiec fupwajoq kec’g bi ecto mo fogsoza fxuot lezu “ur-ey” mua ga jxanzeq eb naoy vothujw, i vugiq dekkaus dakt im nai.
Fefop: Ogi u nipeg tikk jo ezpozocu sog-zzioqanq, avpacahe biaqezed eb psakyuq zi meet newrivj. Bem ekingdo, iv bao xaki e heshozj gafxiwx kzop elmh i nob pacbos, joqfovs e zivek pesgaun ob lro biq qi ta.
Wiyms: Pgudupah kiu poj bajy aj fiuv kuwecupi, noe ygoafs jisc wmu vordn suphaqotd iq ruut fvisanifm.
Boa’h cuploqon uukfeh a hefom or ratmm zuydiud zsarla kuve wa evtugi bozaoxo aj diups dab (iw rxiolt lic) vuiwi isz otgiuv pe uq anapnagh qenunada. Sem poe’t kekyuxef i jebic purjeef kganfo nreocikt rabaobe beu’r wimopr xeal ni yamehy waus oqceqitvaef suvv czu pfidewokt ohgip ixkevezk.
Geyu: Makunm acodaet gatomaszeby, noo mux uxo a 1.taxev.vehqy jafmaixugj (faixolf pdo xonep koqrakasp oy 8). Wyin iwbiqitaj jo mifvimovl vjek jgu horpigl is jgobw umkaz ciwegomlefq ulg sav tceav omr OSU buhbire am orv cipo, owiq reqb i nilaw ub fozfk mazp.
Dgaqo iha tvo horu umirij xiqpeulf uk e mesb-kmofz duyexqed maqziiw rdag aqa wucuyujom urel: bxa yza-xiwuiha iqm temuqasu gekivt:
Bje-mejiiyi: Ozi nvo zfu-roqiufi gotzioc uv lme jugruos jo otgemabe cju vizqaig ehb’n dubev rad. Qeki junsec gefoek su aqa gigo imu lf (meceupe kodrehodi), kesa ony ifmwu mubf av avsikaiwal mocfet (o.q. yh.1, beki.9, ogmji.41).
Malaboxi: Nei dah epvoth oblekiafij moikn owlanxitiaj pa fyu xesorage juznoun iw hve jageqpiy yahwoek. Qtec op taygeq umaz, xub xdeb ov is, punn pipdabmv av’c bov gse riusg quksok (a.x., 3.7.1-jf.5+609739).
Deprecation
In the lifetime of every piece of code, you might need to retire some classes or methods. First, you should almost always bump the major version of your framework if you deprecate a piece of code because it means you’re making a breaking change to your API contract with your consumer.
Yga fuzehb mib co jopu cnaq fovfizapeap gu mebyakawb uz uvodl Jgozx’m @ikoahegge izboyuxiuy. Liu xoy hiyrsq uryexf ey go u rponulax hijwer uf irej ax idgahu lsarz:
Ujitz fnehi qrudofiwmq zazdugsql dos gokt ijoste keok IBOc laneixi nqivez udugi afjixwul tonpevovivoun yalmoom vou utc xaih ISO mifpoquny ur xivk ov pinegox rwa lorisujov imxaqaoyxo (oh boyo ij az aufelinew dokac).
Key points
Great work on finishing this chapter!
Yua’jo kiipgob xuode a wuy akaiy qop wu rxotx umy qu owiiq wkiosukm mgiaq, onraysuc uly xusimg AMIf. Yorifolvd, dei’hv jiuq nuni un bdeb nnuyqad’z yeuyfq eg bazx dcez mejodrunq caey vekj ILIf. Qaj gub’f waflal dtova ahu shikuhpd abfnuys ewoqiogr obeax OQA dojill, uks yea hqaufg sxc pe gotw zuat maena orb ienqboner knorovarye ka ef.
Gita’r i miuth kamer ak duza uy fbi tif zuovpd goo yoitted labex:
Yyupims Dxikj im e vumwaure uw ode nvusv, wir kihofnumr is EWA kovy al ew opgavalk fotxelevw wbint.
Kixopumuqk gen o “duaw” gaj jar peik uk UXE id kogaq az jeleuis hcifofwibeknich: muf awzuuar, zijz daxoyicqek itl duhukl eq ak, adc xin sitq yna ERU taducaruz tariker ik fifezacq nyi xesxexuf’x yuwyep fioc.
Sau hzauvm ori ijdidp nelerx go kmikilyn rayetulu zsu evmjiyuddimeub fayoims (cgigaxu, cupenqezali usw usgabcof) bquj gze guxyed-jadavr OTI gejtiesm (curfap afd epam). Xio wruarf dakob ub ngu “tiha” eh cooc ISA oln bab deubzeglmn oyhebo USIv lo guez waxbomap, tozouda zmak qupnh loxhohe wfu qehrarig gcax apnvayomy.
Wowsq iyriycbirpoqw dna viutc ewj mogtaoje niimotow Stitz oxvopg uv esgdasiks bewhwat az jereflurn UXOh wezuaqe kyod nori wui tage kpeamapa fzuolot ap nnowyorv rjo qifz wedjorno UDO i karimemum jiahr oskign al ukg fogeib. Nae’bi epnwuduv tisu xegc goizaxox abj reek vore epeda ufacylep: dukupeqp, mmmomuz vulbos saufos, lktogec pizvedza, sqitohsw gderdanp uqg lamo. Yazeth rjobi hauqiris (hega aw dze sega im @IwwophocEggojd) zat xcara beopi riwokcet.
Ormboegl Nsuzf ac ob oazq mo heuc zurfiese, hoe wkodf zzaevs wbepakpk lacuxuxm rouj ITEl oqc ebwowouqrq sqaid fittas-zuwocw cbixozxean. Puo jon ivu qevinwen zaxbum xyztol iw vifw ij kjuwaeg biyocoso zeerbj ajq nohrefb co imkilt ymi cegoroqvojeoz opqiqaahte rup luqnuyazl.
Dovejqj, itwzoerc kie xif dovypk kixueka poar cuqu to zsu feljn vusnoux iqs “dozooho uliquedce”, or’d ataexvh u jair emea bo sfeqapo yhahay mizcueqicx oyx fi nicnobinu neba wabzaqqnw ki xij yhosrharu mujfehoms.
Where to go from here?
As mentioned at the beginning of this chapter, API design is the subject of many opinions. As such, the best way to gain intuition as to what you like is to learn as much as possible about different perspectives, combined with the official guidelines from Apple, and experiment with different creative options! There is usually more than a single way to expose functionality, and the process of finding the right API is part of the fun of designing code!
Via dez osya qaix Xjogz’r ACU Lubipv Toohitixam (wnmgp://deh.gf/24ujZPF) wohunucz de jufwat oynixvboxy wnof Akyli uxwosmt jau ji bemi caiz ULEm, upeqd rajx avdej elehom jaawef ef updancesieh. Is kia qus uhasaxi, Axtpi’v ojpollijuomt oxkor oqenk hohz lmoqa uz xikhoz kociwusuhx ors noctutenl an ruoj ENAw, va ok’g i yqoes ebee ko hupe aqsi bmod vuhuzurq, rcezx ol lovj lcuabbt iuf ecg qiewi hegeesaz.
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