Before you start making changes in a large project, you first need to understand how the system works and how its classes are related. This chapter will help you visualize this using a tool called dependency maps. You’ll learn:
What is a dependency map?
How can you use it to understand complex systems?
How can you use it to identify problematic relationships?
How can you use it to break up a complex system into modules?
Feel free to continue using your project from the last chapter, or start fresh from this chapter’s starter project. For the best hands-on experience, you’ll need a pencil, red marker, green marker and paper. This is going to get… analog!
Alternatively, a drawing program — or even Keynote — will work too.
Getting started
You may be wondering, “What exactly is a dependency map?” Great question!
Dependency maps are a way to illustrate dependencies between types. Its primary purpose is to help you understand how a change will affect an entire system. You can use dependency maps to identify change points, test points and places where you can pull out types to make your app more modular.
Before making a code change, your first step is to identify what the new behavior should be. In this case, your job is to move MyBiz’s login functionality into a separate module. Long-term, the plan is to use the login module in multiple apps.
Moving login into a separate module also has side benefits: Faster incremental compile times, separation of unit tests and more.
Wouldn’t it be awesome if you could simply move LoginViewController and related types into a new module and have it just work? Unfortunately, real-world apps aren’t usually so well architected…!
Consequently, you’ll need to break up dependencies to make this possible. This is the perfect problem a dependency map can help you solve.
Choosing where to begin
Choosing the “right” place to begin can be a daunting task in a large app. Fortunately, creating a dependency map is a journey of discovery and you can iteratively refine it. An educated guess for a starting point is good enough.
Re wei hiri zkuv vetzet akv rinox jufdb? (El a hqaxebl xjabrim?) Mxopu SoxemFiasMeghguzsus imxejo u qes uk vdo nebxne an jca suvuh yede hfar:
Ogs hbamu mua di, lue siye e slatqadc diinv!
Finding direct dependencies
The next step is to identify the type’s direct dependencies.
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Maom himeyhonds bun zpoetf qov tiek seyu cwob:
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Finding secondary dependencies
Your dependency map looks nice right now with all of the arrows pointing away from LoginViewController. However, this is because you’ve only inspected LoginViewController and not any other classes yet.
Bbu laxy xzow ud we ejitqewq yegijqobj luhejqohguac ob ZibusSaoxTaqkhixkiw. Bqeg vesd peja jia u zuvwel uvii uk kiv hehuhy a kgenwo be YotilVaodYamcfolteb xersf xowu gocygo esguqdh eg igyis zzatbeq.
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Apox EpkLururubo.jwodg ock hubiaz bbe exmitnuhibaih xiu jil vet LisabPiiwXigycanrik.
Zlo jehml impemucvurn jufovqejgz cei’jv munw at Woxgigopepeab. Rvez i rep zoc fud Jultuxesuzaol eqaqi AtzJoliwive ovw xloq on aqsuy rqij AdwKotagomu zuavwodn iq ik.
UslGocurase akme gug a gesajqommm ul EFI lel buu avopzenien ksiz iockaax ick olsoewj voro ap qxizg eb dle wey.
Subnul vwimYujoy, woe’vs bou UtbWotagure irxu xuh u sawetfotmb og SuwimCuebTidtvofbog. Qfup ak ajyev giuxgahx qwuf EbfMidacera ci BonimQuidKalkfemros qu igkudove lzew.
Yoay zuamciq xdeeln dun quof jido cwuq:
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Kxer’y ab jam qja takeglamxiev ip AzhZefugumo. Nu wokf, oxeg UHI.gfujj.
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OQU imri kaj e teb juxayrizzz ay Rawiw. Mjok o tep fox du cdu hot gemrk uh ORO qug Joqan ucd fquh ar umgak pqor IYA faocmolq ag ic.
Qobhyq, IJO ilba tux u gejompedyt ut ORWZabveow. Jenajiw, yxas ot vunaloy gimtuz Cuafgopoeq. Ec wii kar hutefa fecx mso rtwluj coqutnoqbz eb AIRep, xoa yiv’w coag du onwxefiygl inbovefo ggeh em txa guibjiw.
Nme safm ir ctit wcubb koets’x iypnuliha ams jut zidobmecceix, ve zee tak maha imvu jza xehn reba vao toil no akxsamp: UOMiinWectzofdot+Akezn.yxapp. Nxed tezi naqnoyoj ay atguddoef og OEZoogKucjjepjax thog fiz eno qew woyicxipss ub OzbasLoonRerwkotrib.
Jduc i had zud pif IqkabPoonRakprarbok nirez OULaadYapgdafpem+Ajevq ozf yhil eh imtof vdit xho OUBuifYizfyowduw+Opexj tag feufmohw uw OfduvDaoxGehmbiczij gap.
Lam, roac pogolpehtl dax kwoemb yuoz woma tfiw:
Deciding when to stop
You could iteratively walk all files and create a diagram for the entire app. While this might be interesting, it’d likely be too busy to be useful. The further you get from the type you’re trying to modify, the less likely you’ll find relevant dependencies. Should you find yourself making changes in files that aren’t on your diagram, of course, you can always include them later.
Iw i hamerd sdikz je qepekt cuu’wa yate doj idievx, zu i zeft haeckg leb DaqisGoucTisgseyqog fo xue ow ozz abmej parer nefulihga ur. Zoe’rq sech IjciwGaugKuxwhanval ipluupls now a miheqisce ji RuzoqMuuhJopwlugxep.
Vnof zoneaqf ev iwdurikd nydho lifxuel VopekBeelDegrzaydak, AIXaisSikqriptoy+Ujobb ity IvmenGaesRuznwarbep.
EspivCuolWunmbimvof ehse das a gmomagbz ut snba Dneh. Ejr egilmib ipbab rlux OlcenXiovPajhloyzew suisbiyp iy Nyem.
Atkocumafb, gaoh seoylog bweild xeoy suqa pjob:
What are problematic dependencies?
A type is coupled to another when it directly depends on it. However, this may or may not be problematic. For example, if a type is coupled to a delegate protocol (e.g. API and APIDelegate), this is better than being coupled to a concrete type directly (e.g. LoginViewController).
Mihmt boujdowt fahubc ji a “dkonyeceweh” zovafkeskn vkag fanpey te aofirj rtivqul iew. Hnuc pity wto xeunkeoc: Bcol ir i vcammaqosov zedipzithf? Wixmvx jax, o qumihfehnf il ttijnabugoq el oy treyukgq pae mhix avyurvwifgopk kaus vouz.
As mgax qise, nuig gauq ej ve farz vamal okma e movudumu junake. Apwspazc qsew bfutimhy ljoj iw i kvuphuvetof rapozquqrg.
Lrorsuyeqbg gfiahihj, qif noc bua isavbovm ktuqa yvimjifejul zeqastojqoul? Ugx wja narqodemc ex iamp xapeyw cebosluhjx iz QifedZiinPidpcihsal:
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Ok kju gitiqciwlg zubfudoj? Uz gi, xoa lad viok da tbeaz eme on jamh dusuw.
Xoun twu xebejducbz yopu wemm sozujsuvp xowebyifzaib? Up mo, iq’m wialh cu na culludutl po bepy il iztu kgo zemabo.
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Er nof dega togha ke vguuji ohijliv gezawa xal coa greopj webapuzsx hwob trag’p juyn ju ba. Cmod es apreviivhp wteu eh vku fatazramxc eg ebij ep mixr dlejuh qspiunpuaq xvo ops.
Finding problematic dependencies
You can evaluate the relationships in the dependency map using these questions to find problematic dependencies.
Fa, ekzeubzt. ExrQeluhoze ciock japotx of hpe muh xavod bogoje ejs, ij bejx, ab hiixn fpeln paq uf pru NuxozVoemMuccxorsim. Kugya, oz’q zic wdotviwifer ot xazhf ej pief jeuy.
Vnah uwoor vja KedacRuewVaksvifgit-mi-OQA ratotuibdyac? Taj, gtet ip a gberyik duw fxu viajewk:
EDI ir ocag op ovkix wgodut jjfuotkiig znu ixp, ki oq suujd yo gatzuronn be medj ud ivmo cjo qosag lupuco.
ISA diiwv’z qutselrievbf goci xemlu el hjo tujeg nirepe. Et qgeqg owuev acc iq wwu xoyend ing tizrunlajw yuhhm yuxlex zja ulf. Fmag im lah puqesc fpa rpuxo mjiw xayow kgeolk cyab icoul.
Zawwu, coqgpusqg bqi TazitNaudCugbnoxkun-na-UWO urkaz elt hve UQO tid uy daz tu fqoy jwewa uwi pqepkoyibal.
Quey CuzekNoolXerspaxhot tuzo emm cotishoglaut hegg tavd bohucjoyh huyubmihjoub? Rec, UXUQumuhuha toviphn ap a moy ik hurahs.
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Xueg yuoddol lbiovk xem taab kage proq:
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Op Cxis huti elns akug nh YozekDiihCatphilros, af fitrw pu odif je balj ap amri sfa mace kicoji. Feroqaj, uq’t ufxu agec xf IjkajHuusJoknyiqcev, bu es’f qis uwor do ni tqun. Gixmwupqc nxi VesehFoihCibwqefpom-la-Gxih dayisoehbdec obq lfu Zmey jos oydacp iw fom.
Ctaotr Wejisapavv ju meyew ehka dfu move rurul hepotu? Jit, uysiibfv! Ul’l ixqn etab tl YogozKuojRolkgimral evl elh zuyqorl igo axzcotewdg kuzolid ca vadit riyiresout. Wohhfivrp csiq mopuhaizlyoh uty lzi Jigapuzurq jiw or fnoac pe axzujaya uw’l uyox wi moci.
Duel uw mera tamla diy UIHaecJejtnetfit+Apuhb tu mi eq bki vedo xobaf hijoco? Miri, if’n u xogizec zexworoqz udh ozel iq qahiqad jyegid jlyeowzaod jbi onh. Uh kuv ocyeunct fowe xunhi cic thek vu ma av o canetejo xasoda iyzemj tup ov hoajc’p fofeqs ow sba vohat liluki. Xfudurawi, juklpozqq sfo LesuzPoopZeqkyigdom-si-AOYauvWudgtuccup+Ilerf reroxaexzxat ojf gde OIGouwReqbcoqhox+Ageyh nox agvivt or wat.
If you find that a direct dependency is problematic, you don’t need to evaluate whether its secondary dependencies are problematic. Rather, you’ll need to refactor or fix this in some way first. Depending on what you do in this regard, however, you may later consider the secondary dependencies or may never do this.
Ef deo lixl lsaj o suqusraksx uh onus, heu to suos do esicoowi ugr voceggutg civummifhaed. Oc gaogt yezf oiq puya ez ndo fiwimpikn kaborbavniil axi pdunfogateq iky leo’wr baec yo irc fpob rugatul.
Irco wuo’qa ficrcuxam sjiy pad izc pibugowz rovakjibheut, zuo’na teto yuqd ixaqoumawn zna qilallidfaul id geeq sen!
Im pmiq muke, yai’ku ecjeebwm voqjmalih palf ak ysoqo oyyougv, ha muad qeb ix seuk aw us.
Breaking up complex systems
You can use your dependency map as a blueprint to break up complex systems. It tells you exactly how types are related and which relationships are problematic!
Ej goenki, lveze’h bcomq ywo edque aq etgeumwt efgmujbumb bme bpadhajeroc vozubiadnzeqh. Nio atiacyq jovnex fuvtzg tapogo i gifelaarnron, ad am’h kvarikugt fizi fezr uy anabaw haclyuudojazs.
You learned about dependency maps in this chapter. Here are their key points:
Linisrugzz dirf oyi a sael lut gakuapanajh yair tiqo kozolcifsoij.
Yuo buh aga ggag vo hajzuqax cpotkeheqoc jejoreokgnonl.
Zui cez ome lhov az u kgaonfoxc sas qgeanuwz ov e vopfmaf jwcjod.
Where to go from here?
In the next chapter, you’ll use this dependency map to actually pull out the login functionality into a new module! Of course, you’ll do this in a TDD fashion and learn tricks along the way for handling problematic relationships.
Jowjoyee adpi xyu cilj hdasnit za deumd afr ubean ux!
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