Dependency Injection in Practice (iOSCon)

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!ZPJDIJUHZ Dependency Injection in Practice Yoichi Tagaya iOSCon 2017, London

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!ZPJDIJUHZ Yoichi Tagaya w J04&OHJOFFSBU w $$.BSLFUQMBDFBQQ "WBJMBCMFJO .%PXOMPBETJOUPUBM w )JSJOHJO 4BO'SBODJTDP -POEPO 5PLZP ! " # !"#

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!ZPJDIJUHZ An Author of Swinject • Dependency Injection framework for Swift • Maintained by 5 members • 1.4k+ stars on GitHub • Supporting iOS, macOS, tvOS, watchOS and Linux • 4 extensions provided • github.com/Swinject/Swinject

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!ZPJDIJUHZ Dependency Injection in Practice 1. Basic Concepts 2. Dependency Injection Container 3. Cake Pattern 5PEBZT5BML

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!ZPJDIJUHZ What's Dependency Injection

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!ZPJDIJUHZ What's Dependency Injection Inversion of Control for resolving dependencies You create what you use. ↺ What you use are created and passed.

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!ZPJDIJUHZ What's Dependency Injection Inversion of Control for resolving dependencies You create what you use. ↺ What you use are created and passed. - Initializer Injection (Constructor Injection) - Property Injection - Method Injection Three ways to pass a dependency instance

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!ZPJDIJUHZ Tight Coupling / Loose Coupling Tight Coupling *NQMFNFOUBUJPO $PODSFUF5ZQF &YUFSOBM4ZTUFN OFUXPSL pMFTZTUFN EBUFUJNF SBOEPNOVN

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!ZPJDIJUHZ Tight Coupling / Loose Coupling Tight Coupling *NQMFNFOUBUJPO $PODSFUF5ZQF &YUFSOBM4ZTUFN OFUXPSL pMFTZTUFN EBUFUJNF SBOEPNOVN Hard to test

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!ZPJDIJUHZ Tight Coupling / Loose Coupling Tight Coupling Loose Coupling *NQMFNFOUBUJPO $PODSFUF5ZQF &YUFSOBM4ZTUFN OFUXPSL pMFTZTUFN EBUFUJNF SBOEPNOVN *NQMFNFOUBUJPO $PODSFUF5ZQF &YUFSOBM4ZTUFN *OUFSGBDF 1SPUPDPM Hard to test

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!ZPJDIJUHZ More about Motivation of Dependency Injection IUUQTTLJMMTNBUUFSDPNTLJMMTDBTUTBSDIJUFDUJOHBMJWFBQQT

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!ZPJDIJUHZ Dependency Injection Container (DI Container)

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!ZPJDIJUHZ Problem of Dependency Injection At the beginning... Dependency Injection Code let a = A(b: B()) " Dependency #

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!ZPJDIJUHZ Problem of Dependency Injection Soon... " Dependency # let a = A(b: B(c: C())) $ Dependency Dependency Injection Code

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!ZPJDIJUHZ let a = A(b: B(c: C(f: F()), e: E(f: F()))) Problem of Dependency Injection Much later... $ ' * & # ) " % ( Hard to manage Dependency Injection Code

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!ZPJDIJUHZ Dependency Injection Container $ ' * & # ) " % ( %*$POUBJOFS Dependency Graph Register the dependency graph let a = ... Resolve dependencies upon your request

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!ZPJDIJUHZ Demo Implement a Container 4JNQMF%*$POUBJOFS%FNPIUUQCJUMZPKV 4XJOKFDU%FNPIUUQCJUMZO%[(G7 &%*51MBZHSPVOEQSPHSBNTBSFBWBJMBCMFBU(JU)VC(JTU

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!ZPJDIJUHZ Dependency Injection Container Pros and Cons • Pros - It's easy to use. - Deﬁnitions are in a single place.

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!ZPJDIJUHZ Dependency Injection Container Pros and Cons • Cons &%*51PTTJCMFSVOUJNFFSSPSDBVTFECZGPSDFVOXSBQQJOH

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!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection

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!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection "CTUSBDU $PNQPOFOU "CTUSBDU $PNQPOFOU 1SPUPDPM %FpOFTQMBDFIPMEFS GPSEFQFOEFODZ

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!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection "CTUSBDU $PNQPOFOU "CTUSBDU $PNQPOFOU $PODSFUF $PNQPOFOU $PODSFUF $PNQPOFOU 1SPUPDPM 1SPUPDPM %FpOFTQMBDFIPMEFS GPSEFQFOEFODZ %FpOFTEFQFOEFODZ

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!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection "CTUSBDU $PNQPOFOU "CTUSBDU $PNQPOFOU $POUFYU $PODSFUF $PNQPOFOU $PODSFUF $PNQPOFOU 1SPUPDPM 1SPUPDPM $MBTT4USVDU&OVN %FpOFTQMBDFIPMEFS GPSEFQFOEFODZ %FpOFTEFQFOEFODZ $PNCJOFTEFQFOEFODZ EFpOJUJPOT

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!ZPJDIJUHZ Demo Try Cake Pattern $BLF1BUUFSO%FNPIUUQCJUMZO%RG/K &%*51MBZHSPVOEQSPHSBNJTBWBJMBCMFBU(JU)VC(JTU

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!ZPJDIJUHZ Cake Pattern Pros and Cons • Pros - Lack of deﬁnitions checked by compiler. • Cons - Less easy than DI container. %FQFOEFODZ*OKFDUJPOXJUIUIF$BLF1BUUFSOJO4XJGUCZ#PC$PUUSFMM  IUUQBDRVJIJSFNFEFQFOEFODZJOKFDUJPOXJUIUIFDBLFQBUUFSOJOTXJGU (SFBUBSUJDMFUPMFBSO$BLF1BUUFSO

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!ZPJDIJUHZ Summary • Basic Concepts - Inversion of Control - Tight/loose coupling • Dependency Injection Container - Easy but possible error at runtime • Cake Pattern - Difﬁcult but safe at runtime