Kotlin Multiplatform

Introduction to Kotlin Multiplatform that I gave at Kotlin Everywhere in Minneapolis on October 5, 2019

Transcript

1. Kotlin Multiplatform
   Bryan Herbst
   

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2. Beware: Kotlin MPP
   is under development
   

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3. Why cross-platform?
   

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10. More platforms =
    More developers
    More money
    More code
    More bugs
    

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11. More platforms =
    More developers
    More money
    More code
    More bugs
    

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12. More platforms =
    More developers
    More money
    More code
    More bugs
    

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13. More platforms =
    More developers
    More money
    More code
    More bugs
    

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14. Fewer platforms =
    Fewer developers?
    Less money?
    Less code?
    Fewer bugs?
    

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15. User Experience is table
    stakes
    

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16. User Experience is table
    stakes
    How native is the UI?
    How responsive is the app?
    

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17. User Experience is table
    stakes
    How native is the UI?
    How responsive is the app?
    

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18. Developer happiness is critical
    

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19. Developer happiness is critical
    Speed of platform updates
    Interop with native
    Interop with existing code
    Language
    

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20. Developer happiness is critical
    Speed of platform updates
    Interop with native
    Interop with existing code
    Language
    

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21. Developer happiness is critical
    Speed of platform updates
    Interop with native
    Interop with existing code
    Language
    

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22. Developer happiness is critical
    Speed of platform updates
    Interop with native
    Interop with existing code
    Language
    

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23. Cross-platform architecture
    

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24. What to share?
    

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25. As much (or as little)
    as you want
    

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26. Embrace platform differences,
    but provide a consistent core
    

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27. Assumption: you already
    have an iOS & Android app
    

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28. Feature
    UI
    Logic
    Data
    

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29. Feature
    UI
    Logic
    Data
    Data models,
    Networking
    

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30. Feature
    UI
    Logic
    Data
    Great place to
    start!
    

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31. Feature
    UI
    Logic
    Data
    ViewControllers,
    ViewModels
    

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32. Feature
    UI
    Logic
    Data
    Trickier
    

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33. Feature
    UI
    Logic
    Data
    Layouts, Views
    

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34. Feature
    UI
    Logic
    Data
    Probably not
    worth it
    

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35. What is platform dependent?
    

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36. What is platform dependent?
    Almost everything the user sees
    

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37. What is platform dependent?
    Logging
    

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38. What is platform dependent?
    Disk storage
    

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39. What is platform dependent?
    Networking
    

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40. Shared Library
    Common
    Android iOS
    

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41. Shared Library
    Common
    Android iOS
    Android
    App
    iOS
    App
    

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42. Shared Library
    Common
    Android iOS
    Android
    App
    iOS
    App
    lib lib
    

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43. Mono Repo
    Common
    Android iOS
    Android
    App
    iOS
    App
    lib lib
    

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44. Shared Library
    Common
    Android iOS
    Android
    App
    iOS
    App
    lib lib
    

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45. How Kotlin MPP works
    

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46. kotlinc
    Main.kt
    

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47. kotlinc
    Frontend
    Intermediate
    representation
    Backend
    

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48. kotlinc
    Frontend
    Intermediate
    representation
    Backend
    

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49. kotlinc
    Frontend
    Intermediate
    representation
    Backend
    

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50. kotlinc
    Frontend
    Intermediate
    representation
    Kotlin JVM
    

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51. kotlinc
    Frontend
    Intermediate
    representation
    Kotlin JS
    

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52. kotlinc
    Frontend
    Intermediate
    representation
    Kotlin Native
    

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53. Kotlin JVM
    Output is bytecode
    

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54. Kotlin JVM
    100% interoperability
    

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55. Kotlin JS
    Output is JS
    

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56. Kotlin JS
    Output is JS
    

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57. Kotlin JS - libraries
    Dukat binds strongly-typed libraries
    

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58. Kotlin JS - libraries
    dynamic type supports loose typing
    

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59. Dynamic
    val dyn: dynamic = ...
    

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60. Dynamic
    Disables type checking
    

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61. Dynamic
    Can call any property or function
    

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62. Kotlin Native
    Outputs native binary
    

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63. Kotlin Native
    Outputs native binary
    Executable
    

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64. Kotlin Native
    Outputs native binary
    Executable
    C library
    

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65. Kotlin Native
    Outputs native binary
    Executable
    C library
    Apple framework
    

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66. Kotlin Native
    Compiled with LLVM
    

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67. Kotlin Native
    arm32, arm64
    x86, x86_64
    mingw x86_64
    MIPS, rPi
    wasm32
    

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68. Native libraries
    1. Create .def
    2. Cinterop creates kotlin bindings of
    C/C++ code
    

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69. Native libraries
    1. Create .def
    2. cinterop produces Kotlin bindings
    

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70. Native libraries
    Platform libraries
    

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71. Native libraries
    Platform libraries
    e.g. Open GL, objc, posix
    

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72. Swift?
    

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73. Kotlin Multiplatform
    

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74. Main.kt Frontend IR
    JVM
    Native
    JS
    

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75. Let’s get started!
    

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76. plugins {
    id 'org.jetbrains.kotlin.multiplatform'
    version '1.3.50’
    }
    

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77. kotlin {
    jvm() // Creates a JVM target
    }
    

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78. kotlin {
    iosArm32("ios32")
    iosArm64("ios64")
    configure([ios32, ios64]) {
    binaries.framework {
    baseName = "SharedCode"
    }
    }
    }
    

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79. kotlin {
    iosArm32("ios32")
    iosArm64("ios64")
    configure([ios32, ios64]) {
    binaries.framework {
    baseName = "SharedCode"
    }
    }
    }
    

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80. kotlin {
    iosArm32("ios32")
    iosArm64("ios64")
    // Simulator
    iosX64("iosX64")
    }
    

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81. val sdk = System.getenv("SDK_NAME")
    if (sdk?.startsWith("iphoneos")) {
    iosX64("iosX64")
    } else {
    //....
    }
    

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82. Carthage or CocoaPods
    

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83. plugins {
    id("org.jetbrains.kotlin.native.cocoapods")
    }
    kotlin {
    cocoapods {
    summary = "Shared library"
    homepage = "http://github.com/shared-lib"
    }
    }
    

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84. Time to write some code
    

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85. Android
    Notes UI
    NotesView
    Model
    Note (model)
    Note API
    iOS
    Notes UI
    NotesView
    Controller
    Note (model)
    Note API
    

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86. Android
    Notes UI
    NotesView
    Model
    Note API
    iOS
    Notes UI
    NotesView
    Controller
    Note API
    Shared
    Note (model)
    

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87. Note JSON
    {
    content: "Hello",
    status: "Pinned"
    }
    

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88. iOS
    struct Note {
    let content: String
    let status: String
    }
    Android
    data class Note(
    val content: String,
    val status: Status
    )
    enum class Status { }
    

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89. iOS
    struct Note {
    let content: String
    let status: String
    }
    Android
    data class Note(
    val content: String,
    val status: Status
    )
    enum class Status { }
    

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90. iOS
    struct Note {
    let content: String
    let status: String
    }
    Android
    data class Note(
    val content: String,
    val status: Status
    )
    enum class Status { }
    

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91. data class Note(
    val content: String,
    val status: String
    )
    Shared
    

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92. data class Note(
    val content: String,
    val status: String
    )
    Android
    

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93. __attribute__((objc_subclassing_restricted))
    __attribute__((swift_name("Note")))
    @interface SharedNote : KotlinBase
    @property (readonly) NSString * content;
    @property (readonly) NSString * status;
    @end;
    iOS
    

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94. __attribute__((objc_subclassing_restricted))
    __attribute__((swift_name("Note")))
    @interface SharedNote : KotlinBase
    @property (readonly) NSString * content;
    @property (readonly) NSString * status;
    @end;
    iOS
    

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95. __attribute__((objc_subclassing_restricted))
    __attribute__((swift_name("Note")))
    @interface SharedNote : KotlinBase
    @property (readonly) NSString * content;
    @property (readonly) NSString * status;
    @end;
    iOS – Objective C
    

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96. class Note: KotlinBase {
    private(set) var content: String?
    private(set) var status: String?
    }
    iOS – Swift
    

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97. Android
    Notes UI
    NotesView
    Model
    Note API
    iOS
    Notes UI
    NotesView
    Controller
    Note API
    Shared
    Note (model)
    

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98. Android
    Notes UI
    NotesView
    Model
    iOS
    Notes UI
    NotesView
    Controller
    Shared
    Note (model)
    Note API
    

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99. Serialization
    Kotlinx.serialization
    

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100. @Serializable
     data class Note(
     val content: String
     val status: String
     )
     

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101. Json.nonstrict
     .stringify(
     Note.serializer(),
     note
     )
     

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102. Json.nonstrict
     .parse(
     Note.serializer(),
     jsonString
     )
     

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103. Json.nonstrict
     .parse(
     Note.serializer().list,
     jsonString
     )
     

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104. Serialization is multiplatform!
     

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105. Serialization is multiplatform!
     Charsets, input streams, buffers
     

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106. commonMain {
     dependencies {
     implementation "serialization-runtime-common"
     }
     }
     

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107. jvmMain {
     dependencies {
     implementation "serialization-runtime"
     }
     }
     

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108. nativeMain {
     dependencies {
     implementation "serialization-runtime-native"
     }
     }
     

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109. Networking
     KTOR
     

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110. Under the hood - engines
     Android: OkHttp, HttpUrlConnection
     

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111. Under the hood - engines
     Android: OkHttp, HttpUrlConnection
     iOS: NSUrlSession
     

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112. class NoteApi() {
     private val client = HttpClient()
     suspend fun fetchNote(): String
     = client.get("http://...")
     }
     

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113. How do we support
     different platforms?
     

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114. common/PlatformName.kt
     expect fun getPlatform(): String
     

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115. android/PlatformName.kt
     actual fun getPlatform()= "Android"
     

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116. ios/PlatformName.kt
     actual fun getPlatform() = "iOS"
     

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117. Common/KeyValueStore.kt
     expect class KeyValueStore() {
     fun setString(key: String, value: String)
     fun getString(key: String): String
     }
     

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118. android/KeyValueStore.kt
     actual class KeyValueStore() {
     private val prefs: SharedPreferences
     actual fun setString() //...
     actual fun getString() //...
     }
     

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119. ios/KeyValueStore.kt
     actual class KeyValueStore() {
     private val userDefaults: NSUserDefaults
     actual fun setString() //...
     actual fun getString() //...
     }
     

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120. expect interface Closeable {
     fun close()
     }
     actual typealias Closeable = java.io.Closeable
     

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121. Platform differences
     

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123. Unsupported in Swift/Obj-C
     Suspend functions
     Inline classes
     

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124. Asyncronous work
     

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125. Coroutines
     Only single-threaded code is currently
     supported for Kotlin/Native
     

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126. Exceptions
     

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127. Exceptions
     All Kotlin exceptions are unchecked
     

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128. Exceptions
     All Kotlin exceptions are unchecked
     Swift only has checked errors
     

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129. Exceptions
     Annotate with @Throws
     

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130. Primitive types
     Int -> KotlinInt
     

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131. Primitive types
     Int -> KotlinInt (NSNumber)
     

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132. Generics
     

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133. Generics
     Experimental for Kotlin Native
     

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134. Generics
     Experimental for Kotlin Native
     extraOpts "-Xobjc-generics"
     

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135. Kotlin:
     class Generic
     Swift:
     class Generic
     

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136. Kotlin:
     class Generic
     Swift:
     class Generic
     

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137. Kotlin:
     class Generic(val item: T)
     Swift:
     class Generic {
     let item: T?
     }
     

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138. Kotlin:
     class Generic(val item: T)
     Swift:
     class Generic {
     let item: T?
     }
     ?
     

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139. Kotlin:
     class Generic(val item: T)
     Swift:
     class Generic {
     let item: T
     }
     

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140. Thanks!
     

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