Dependency Injection in Practice (iOSCon)

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

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

!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

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

!ZPJDIJUHZ What's Dependency Injection

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

!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

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

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

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

*NQMFNFOUBUJPO $PODSFUF5ZQF &YUFSOBM4ZTUFN OFUXPSL pMFTZTUFN EBUFUJNF SBOEPNOVN *NQMFNFOUBUJPO $PODSFUF5ZQF &YUFSOBM4ZTUFN *OUFSGBDF 1SPUPDPM .PDL Hard to test

*NQMFNFOUBUJPO $PODSFUF5ZQF &YUFSOBM4ZTUFN OFUXPSL pMFTZTUFN EBUFUJNF SBOEPNOVN *NQMFNFOUBUJPO $PODSFUF5ZQF &YUFSOBM4ZTUFN *OUFSGBDF 1SPUPDPM .PDL Hard to test Easy to test

!ZPJDIJUHZ More about Motivation of Dependency Injection IUUQTTLJMMTNBUUFSDPNTLJMMTDBTUTBSDIJUFDUJOHBMJWFBQQT

!ZPJDIJUHZ Dependency Injection Container (DI Container)

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

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

!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

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

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

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

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

!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection

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

$PNQPOFOU $PODSFUF $PNQPOFOU $PODSFUF $PNQPOFOU 1SPUPDPM 1SPUPDPM %FpOFTQMBDFIPMEFS GPSEFQFOEFODZ %FpOFTEFQFOEFODZ

$PNQPOFOU $POUFYU $PODSFUF $PNQPOFOU $PODSFUF $PNQPOFOU 1SPUPDPM 1SPUPDPM $MBTT4USVDU&OVN %FpOFTQMBDFIPMEFS GPSEFQFOEFODZ %FpOFTEFQFOEFODZ $PNCJOFTEFQFOEFODZ EFpOJUJPOT

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

!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

!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

Dependency Injection in Practice (iOSCon)

Dependency Injection in Practice (iOSCon)

Yoichi Tagaya

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

!ZPJDIJUHZ Yoichi Tagaya w J04&OHJOFFSBU w $$.BSLFUQMBDFBQQ "WBJMBCMFJO

!ZPJDIJUHZ An Author of Swinject • Dependency Injection framework for

!ZPJDIJUHZ Dependency Injection in Practice 1. Basic Concepts 2. Dependency

!ZPJDIJUHZ What's Dependency Injection

!ZPJDIJUHZ What's Dependency Injection Inversion of Control for resolving dependencies

!ZPJDIJUHZ What's Dependency Injection Inversion of Control for resolving dependencies

!ZPJDIJUHZ Tight Coupling / Loose Coupling Tight Coupling *NQMFNFOUBUJPO $PODSFUF5ZQF

!ZPJDIJUHZ Tight Coupling / Loose Coupling Tight Coupling *NQMFNFOUBUJPO $PODSFUF5ZQF

!ZPJDIJUHZ Tight Coupling / Loose Coupling Tight Coupling Loose Coupling

!ZPJDIJUHZ Tight Coupling / Loose Coupling Tight Coupling Loose Coupling

!ZPJDIJUHZ Tight Coupling / Loose Coupling Tight Coupling Loose Coupling

!ZPJDIJUHZ More about Motivation of Dependency Injection IUUQTTLJMMTNBUUFSDPNTLJMMTDBTUTBSDIJUFDUJOHBMJWFBQQT

!ZPJDIJUHZ Dependency Injection Container (DI Container)

!ZPJDIJUHZ Problem of Dependency Injection At the beginning... Dependency Injection

!ZPJDIJUHZ Problem of Dependency Injection Soon... " Dependency # let

!ZPJDIJUHZ let a = A(b: B(c: C(f: F()), e: E(f:

!ZPJDIJUHZ Dependency Injection Container $ ' * & # )

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

!ZPJDIJUHZ Dependency Injection Container Pros and Cons • Pros -

!ZPJDIJUHZ Dependency Injection Container Pros and Cons • Cons

!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection

!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection "CTUSBDU $PNQPOFOU "CTUSBDU

!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection "CTUSBDU $PNQPOFOU "CTUSBDU

!ZPJDIJUHZ Cake Pattern: Statically Deﬁned Dependency Injection "CTUSBDU $PNQPOFOU "CTUSBDU

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

!ZPJDIJUHZ Cake Pattern Pros and Cons • Pros - Lack

!ZPJDIJUHZ Summary • Basic Concepts - Inversion of Control -