Troubled Waters: Bridging platform-native SDKs with Kotlin Multiplatform

Talking to native APIs from Kotlin Multiplatform (mostly) Mobile.

Transcript

1. Troubled Waters:
   Bridging platform-native SDKs
   with Kotlin Multiplatform
   Kevin Galligan
   

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2. Partner at
   Kotlin GDE
   

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3. Touchlab
   

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5. Common
   JVM JS Native
   

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6. Common
   JVM JS Native
   Firebase/JVM
   Firebase/JS
   Firebase/iOS
   

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8. Common
   JVM JS Native
   Firebase/JVM
   Firebase/JS
   Firebase/iOS
   

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9. Common
   Android iOS
   Firebase/JVM Firebase/iOS
   

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10. JNI
    

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11. Basic Topics
    • Tell Kotlin about the native code
    • Link native code into Kotlin Xcode Framework
    • API Design
    

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12. Simple First
    pass it in
    

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13. Interface Driven
    • 💰 Don’t need cinterop
    • 💰 No weird linking
    • 💰 No extra binary size
    • 🗑 Not easily testable
    • 🗑 Impractical for complex situations
    • 🗑 Bad for libraries
    

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14. interface KotlinAnalytics {
    fun logEvent(name: String, parameters: Map)
    }
    

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15. interface KotlinAnalytics {
    fun logEvent(name: String, parameters: Map)
    }
    fun initKoinIos(
    userDefaults: NSUserDefaults,
    appInfo: AppInfo,
    analytics: KotlinAnalytics,
    doOnStartup: () -> Unit
    ) (
    // Etc
    )
    

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16. class IosAnalytics: KotlinAnalytics {
    
    
    func logEvent(name: String, parameters: [String : Any]) {
    
    
    Analytics.logEvent(name, parameters: parameters)
    
    
    }
    
    
    }
    

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17. class IosAnalytics: KotlinAnalytics {
    
    
    func logEvent(name: String, parameters: [String : Any]) {
    
    
    Analytics.logEvent(name, parameters: parameters)
    
    
    }
    
    
    }
    KoinIOSKt.doInitKoinIos(
    
    
    userDefaults: userDefaults,
    
    
    appInfo: iosAppInfo,
    
    
    analytics: IosAnalytics(),
    
    
    doOnStartup: doOnStartup
    
    
    )
    

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18. fun withCallback(callback: (Breed) -> Unit) {
    }
    

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19. viewModel.withCallback(callback: {[weak self] (breed:Breed) -> Void in
    
    
    self?.callMe(breed: breed)
    
    
    })
    

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20. cinterop
    kotlin calling c/objc
    

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21. cinterop
    kotlin calling c/objc
    

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22. Call C/Obj-C
    some swift, some C++
    

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23. *.h cinterop Kotlin/iOS
    

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24. *.h cinterop Kotlin/iOS
    Binary
    ? ?
    ? ? ?
    ?
    ?
    ? ?? ?
    ?
    

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25. package = co.touchlab.whatever
    language = Objective-C
    headers = whatever.h
    whatever.def
    

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26. other config
    

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27. package = co.touchlab.whatever
    language = Objective-C
    headers = whatever.h
    whatever.def
    

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28. extraOpts = listOf("-mode", "sourcecode")
    

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29. *.h cinterop Kotlin/iOS
    Binary
    ? ?
    ? ? ?
    ?
    ?
    ? ?? ?
    ?
    

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30. Where are these *.h files?
    multiple options
    

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31. In Your Repo
    copy/paste
    

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33. Script Downloads
    grab headers
    

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34. Truncated Headers
    feels like cheating a bit :)
    

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36. Cocoapods Dependency
    the hammer approach
    

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37. kotlin {
    //etc
    cocoapods {
    summary = "Common library for the KaMP starter kit"
    homepage = "https://github.com/touchlab/KaMPKit"
    ios.deploymentTarget = "12.4"
    podfile = project.file("../ios/Podfile")
    pod("FirebaseAnalytics")
    }
    }
    

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38. Docs on Cocoapods/Kotlin
    https://kotlinlang.org/docs/native-cocoapods-libraries.html
    

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39. cocoapods.FirebaseAnalytics
    .FIRAnalytics.logEventWithName("someevent", mapOf(/*data*/))
    

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40. Makes project weird
    can’t run tests, dependency in podspec
    

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41. Carthage ❤ Kotlin
    https://github.com/wireapp/carthage-gradle-plugin
    

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42. SPM?
    not yet
    

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43. Linking
    where is the binary?
    

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44. *.h cinterop Kotlin/iOS
    Binary
    ? ?
    ? ? ?
    ?
    ?
    ? ?? ?
    ?
    

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45. complex-ish
    

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48. Linking Basics
    Binary
    Framework
    

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49. Static Linking
    Binary
    Static Framework
    

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50. Dynamic Linking
    Binary
    Dynamic Framework
    

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51. Assemble Static
    Static Framework
    *.h cinterop Kotlin/iOS
    Binary
    ? ?
    ? ? ?
    ?
    ?
    ??? ?
    ?
    

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52. Assemble Dynamic
    *.h cinterop Kotlin/iOS
    Binary
    ? ?
    ? ? ?
    ?
    ?
    ??? ?
    ?
    Dynamic Framework
    

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53. Libraries == More Complex
    recency bias
    

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54. Kermit
    Crashlytics
    Firebase.h
    Firebase
    

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55. Kermit
    Crashlytics
    Firebase.h
    Firebase
    Dynamic
    

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56. Undefined symbols for architecture x86_64:
    
    
    "_OBJC_CLASS_$_FIRStackFrame", referenced from:
    
    
    objc-class-ref in libco.touchlab:kermit-crashlytics-cache.a(result.o)
    
    
    "_OBJC_CLASS_$_FIRExceptionModel", referenced from:
    
    
    objc-class-ref in libco.touchlab:kermit-crashlytics-cache.a(result.o)
    
    
    "_OBJC_CLASS_$_FIRCrashlytics", referenced from:
    
    
    objc-class-ref in libco.touchlab:kermit-crashlytics-cache.a(result.o)
    
    
    ld: symbol(s) not found for architecture x86_64
    
    
    

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57. Undefined symbols for architecture x86_64:
    
    
    "_OBJC_CLASS_$_FIRStackFrame", referenced from:
    
    
    objc-class-ref in libco.touchlab:kermit-crashlytics-cache.a(result.o)
    
    
    "_OBJC_CLASS_$_FIRExceptionModel", referenced from:
    
    
    objc-class-ref in libco.touchlab:kermit-crashlytics-cache.a(result.o)
    
    
    "_OBJC_CLASS_$_FIRCrashlytics", referenced from:
    
    
    objc-class-ref in libco.touchlab:kermit-crashlytics-cache.a(result.o)
    
    
    ld: symbol(s) not found for architecture x86_64
    
    
    

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58. stay one lesson ahead…
    

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59. Kotlin/iOS
    Cocoapods
    *.h
    Binary
    

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60. Kotlin/iOS
    Some Code
    *.h
    *.c/*.m
    

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61. Kotlin/iOS
    *.h *.c/*.m
    cinterop clang
    

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62. Kotlin/iOS
    *.h *.c/*.m
    cinterop
    

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63. Kotlin/iOS
    *.h *.c/*.m
    cinterop cklib
    

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64. cklib Links
    • https://github.com/touchlab/cklib
    • https://github.com/cashapp/zipline/blob/trunk/
    zipline/build.gradle.kts#L157
    • https://github.com/touchlab/Kermit/blob/main/
    kermit-crashlytics-test/build.gradle.kts#L69
    

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65. Linking Links
    • https://bpoplauschi.github.io/2021/10/24/Intro-to-static-and-dynamic-
    libraries-frameworks.html
    • https://bpoplauschi.github.io/2021/10/25/Advanced-static-vs-dynamic-
    libraries-and-frameworks.html
    

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66. Testing
    Binary
    Framework
    

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67. Kotlin/iOS
    test.kexe
    

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68. Kotlin/iOS
    test.kexe
    Cocoapods
    *.h
    Binary Some Code
    *.h
    *.c/*.m
    

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69. Kotlin/iOS
    test.kexe
    *.h
    Binary
    Firebase.h
    Firebase
    

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70. Kotlin/iOS
    test.kexe
    *.h
    Binary
    Firebase.h
    Firebase
    Stub Binary
    

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72. Kotlin/iOS
    test.kexe
    *.h
    Binary
    Firebase.h
    Firebase
    Stub Binary
    

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73. stay one lesson ahead…
    

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74. API Design
    thoughts on the common language
    

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75. Uncanny Valley
    they do the same thing, but…
    

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76. Common
    Android iOS
    Firebase/JVM Firebase/iOS
    

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77. Common
    Android iOS
    Firebase/JVM Firebase/iOS
    

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78. Common
    Android iOS
    C code
    

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79. Common
    Android iOS
    C code
    JNI cinterop
    bridge
    

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80. Common
    Android iOS
    C code
    JNI cinterop
    bridge
    

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81. Rules are difficult
    “it depends” is everything
    

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82. Don’t default expect/actual
    can be good, can be frustrating
    

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83. expect/actual is less flexible
    harder to test, etc
    

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84. expect class KotlinAnalytics() {
    fun logEvent(name: String, parameters: Map)
    }
    

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85. interface KotlinAnalytics {
    fun logEvent(name: String, parameters: Map)
    }
    expect fun platformAnalyticsFactory(): KotlinAnalytics
    

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87. expect fun platformLogWriter(): LogWriter
    

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88. expect class CrashlyticsLogWriter(
    minSeverity: Severity = Severity.Info,
    minCrashSeverity: Severity = Severity.Warn,
    printTag: Boolean = true
    ) : LogWriter
    

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89. expect fun crashlyticsLogWriter(
    minSeverity: Severity = Severity.Info,
    minCrashSeverity: Severity = Severity.Warn,
    printTag: Boolean = true
    ) : LogWriter
    

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90. Service Objects/Small Graph
    interface and delegates work well
    

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91. Parent<->Child/Larger Graph
    interface-with-delegates starts looking ugly
    

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92. Order
    Big Graph/Data Objects
    getProducts() Product
    Product
    Product
    Supplier
    

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93. Order
    Big Graph/Data Objects
    getProducts() Product
    Product
    Product
    Supplier
    

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94. actual typealias
    with great power…
    

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95. /**
    
    
    * Multiplatform AtomicInt implementation
    
    
    */
    
    
    expect class AtomicInt(initialValue: Int) {
    
    
    fun get(): Int
    
    
    fun set(newValue: Int)
    
    
    fun incrementAndGet(): Int
    
    
    fun decrementAndGet(): Int
    
    
    fun addAndGet(delta: Int): Int
    
    
    fun compareAndSet(expected: Int, new: Int): Boolean
    
    
    }
    

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96. JVM Side?
    

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97. import java.util.concurrent.atomic.AtomicInteger
    
    
    actual typealias AtomicInt = AtomicInteger
    

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98. Actual needs to match
    because obviously it does
    

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99. import kotlin.native.concurrent.AtomicInt
    
    
    actual class AtomicInt actual constructor(initialValue:Int){
    
    
    private val atom = AtomicInt(initialValue)
    
    
    
    
    actual fun get(): Int = atom.value
    
    
    actual fun set(newValue: Int) {
    
    
    atom.value = newValue
    
    
    }
    
    
    actual fun incrementAndGet(): Int = atom.addAndGet(1)
    
    
    actual fun decrementAndGet(): Int = atom.addAndGet(-1)
    
    
    actual fun addAndGet(delta: Int): Int = atom.addAndGet(delta)
    
    
    actual fun compareAndSet(expected: Int, new: Int): Boolean =
    atom.compareAndSet(expected, new)
    
    
    }
    

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100. import kotlin.native.concurrent.AtomicInt
     
     
     actual class AtomicInt actual constructor(initialValue:Int){
     
     
     private val atom = AtomicInt(initialValue)
     
     
     
     
     actual fun get(): Int = atom.value
     
     
     actual fun set(newValue: Int) {
     
     
     atom.value = newValue
     
     
     }
     
     
     actual fun incrementAndGet(): Int = atom.addAndGet(1)
     
     
     actual fun decrementAndGet(): Int = atom.addAndGet(-1)
     
     
     actual fun addAndGet(delta: Int): Int = atom.addAndGet(delta)
     
     
     actual fun compareAndSet(expected: Int, new: Int): Boolean =
     atom.compareAndSet(expected, new)
     
     
     }
     

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101. Platform Affinity
     android iOS
     ?
     

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102. Platform Affinity
     android iOS
     android-y
     

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103. typealias can be brittle
     

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104. typealias can be brittle
     

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105. Platform Affinity
     android iOS
     android-y
     JS
     

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106. Parallel Delegates
     android iOS
     android-y
     

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107. Empty Typealias
     everything is extensions
     

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108. expect class QuerySnapshot
     
     
     expect val QuerySnapshot.documentChanges_:List
     
     
     expect fun QuerySnapshot.getDocumentChanges_(…):List
     
     
     expect val QuerySnapshot.documents_:List
     
     
     expect val QuerySnapshot.metadata: SnapshotMetadata
     
     
     expect val QuerySnapshot.query: Query
     
     
     expect val QuerySnapshot.empty: Boolean
     
     
     expect val QuerySnapshot.size: Int
     

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109. expect class QuerySnapshot
     
     
     expect val QuerySnapshot.documentChanges_:List
     
     
     expect fun QuerySnapshot.getDocumentChanges_(…):List
     
     
     expect val QuerySnapshot.documents_:List
     
     
     expect val QuerySnapshot.metadata: SnapshotMetadata
     
     
     expect val QuerySnapshot.query: Query
     
     
     expect val QuerySnapshot.empty: Boolean
     
     
     expect val QuerySnapshot.size: Int
     

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110. actual typealias QuerySnapshot = FIRQuerySnapshot
     
     
     actual val QuerySnapshot.documentChanges_: List
     
     
     get() = documentChanges as List
     
     
     actual val QuerySnapshot.documents_: List
     
     
     get() = documents as List
     
     
     actual fun QuerySnapshot.getDocumentChanges_(metadataChanges: Metadata
     documentChangesWithIncludeMetadataChanges(metadataChanges == Metad
     iOS
     

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111. actual typealias QuerySnapshot = FIRQuerySnapshot
     
     
     actual val QuerySnapshot.documentChanges_: List
     
     
     get() = documentChanges as List
     
     
     actual val QuerySnapshot.documents_: List
     
     
     get() = documents as List
     
     
     actual fun QuerySnapshot.getDocumentChanges_(metadataChanges: Metadata
     documentChangesWithIncludeMetadataChanges(metadataChanges == Metad
     iOS
     

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112. actual typealias QuerySnapshot = FIRQuerySnapshot
     
     
     actual val QuerySnapshot.documentChanges_: List
     
     
     get() = documentChanges as List
     
     
     actual val QuerySnapshot.documents_: List
     
     
     get() = documents as List
     
     
     actual fun QuerySnapshot.getDocumentChanges_(metadataChanges: Metadata
     documentChangesWithIncludeMetadataChanges(metadataChanges == Metad
     iOS
     

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113. expect open class DocumentSnapshot
     DocumentSnapshot
     actual typealias DocumentSnapshot = FIRDocumentSnapshot
     iOS
     common
     actual typealias DocumentSnapshot =
     com.google.firebase.firestore.DocumentSnapshot
     Android
     

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114. actual typealias QuerySnapshot = com.google.firebase.firestore.QuerySn
     actual val QuerySnapshot.documentChanges_: List
     
     
     get() = documentChanges
     
     
     actual val QuerySnapshot.documents_: List
     
     
     get() = documents
     
     
     actual fun QuerySnapshot.getDocumentChanges_(metadataChanges: Metadata
     getDocumentChanges(metadataChanges.toJvm())
     Android
     

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115. Platform Affinity
     

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116. Platform Agnostic
     

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117. Order
     Big Graph/Data Objects
     getProducts() Product
     Product
     Product
     Supplier
     

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118. Order
     Big Graph/Data Objects
     getProducts() Product
     Product
     Product
     Supplier
     

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119. Again, that’s rare
     mostly just use interfaces and delegates!
     

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120. Empty Typealias
     • https://vimeo.com/371460823
     • https://github.com/touchlab-lab/FirestoreKMP
     

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122. API *almost* designs itself
     you’re mapping existing APIs
     

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123. Iterative Design
     tweak for platform specifics
     

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124. Platform-Specific Init
     then common
     

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125. Whatever/
     Common
     Whatever/
     Android
     Whatever/
     iOS
     Whatever
     AAR Whatever.h
     Init Init
     

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126. Whatever/
     Common
     Whatever/
     Android
     Whatever/
     iOS
     Whatever
     AAR Whatever.h
     Init Init
     Other Calls
     

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127. Simple First
     pass it in
     

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128. That was a lot!
     it’s not all that bad
     

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129. At Touchlab
     • Big team build tools
     • Better iOS Dev ex
     • Swift code generation
     • Other things
     

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130. If you’re facing these issues…
     @kpgalligan
     Kotlin Slack
     

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131. Thanks!
     @kpgalligan
     

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132. Thanks!
     @kpgalligan
     Join the team
     !
     

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