Mastering API Visibility in Kotlin (Rheinwerk Konferenz für Kotlin 2021)

When designing a library, minimizing your API surface - the types, methods, properties, and functions you expose to the outside world - is a great idea. This doesn't apply to just libraries: it's a consideration you should make for every module in a multi-module project. In this talk, we'll look at all the ways that Kotlin lets you get your visibility just right.

Resources and more: https://zsmb.co/talks/mastering-api-visibility/

Transcript

1. Márton Braun
   zsmb.co
   zsmb13
   Mastering API
   Visibility in Kotlin
   

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2. API surface
   

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3. API surface
   

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4. API surface
   

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5. API surface
   

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6. API surface
   

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7. API surface
   

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8. API surface
   

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9. API surface
   

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10. API surface
    

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11. API surface
    

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12. API surface
    

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13. API surface
    

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14. API surface
    

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15. API surface
    

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16. API surface
    

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17. API surface
    

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18. API surface
    

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19. Minimal APIs
    

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20. Minimal APIs
    Item 15: Minimize the accessibility of classes and members
    

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21. Minimal APIs
    Item 15: Minimize the accessibility of classes and members
    Chapter 4: Classes and Interfaces
    

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22. Minimal APIs
    › Easier to maintain and change
    

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23. Minimal APIs
    › Easier to maintain and change
    

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24. Minimal APIs
    › Easier to maintain and change
    

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25. Minimal APIs
    › Easier to maintain and change
    

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26. Minimal APIs
    › Easier to maintain and change
    

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27. Minimal APIs
    › Easier to maintain and change
    

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28. Minimal APIs
    › Easier to maintain and change
    

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29. Minimal APIs
    › Easier to maintain and change
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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30. replaceWith = ReplaceWith(
    "this.stringPref(key).validate(isValid)",
    ),
    Minimal APIs
    › Easier to maintain and change
    @Deprecated(
    message = "Use a chained .validate {} call instead",
    level = DeprecationLevel.WARNING,
    )
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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31. replaceWith = ReplaceWith(
    "this.stringPref(key).validate(isValid)",
    ),
    Minimal APIs
    › Easier to maintain and change
    @Deprecated(
    message = "Use a chained .validate {} call instead",
    level = DeprecationLevel.WARNING,
    )
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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32. replaceWith = ReplaceWith(
    "this.stringPref(key).validate(isValid)",
    ),
    Minimal APIs
    › Easier to maintain and change
    @Deprecated(
    message = "Use a chained .validate {} call instead",
    level = DeprecationLevel.WARNING,
    )
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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33. Minimal APIs
    › Easier to maintain and change @Deprecated(
    message = "Use a chained .validate {} call instead",
    level = DeprecationLevel.WARNING,
    replaceWith = ReplaceWith(
    "this.stringPref(key).validate(isValid)",
    imports = arrayOf("com.example.validate"),
    ),
    )
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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34. Minimal APIs
    › Easier to maintain and change @Deprecated(
    message = "Use a chained .validate {} call instead",
    level = DeprecationLevel.ERROR,
    replaceWith = ReplaceWith(
    "this.stringPref(key).validate(isValid)",
    imports = arrayOf("com.example.validate"),
    ),
    )
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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35. Minimal APIs
    › Easier to maintain and change @Deprecated(
    message = "Use a chained .validate {} call instead",
    level = DeprecationLevel.ERROR,
    replaceWith = ReplaceWith(
    "this.stringPref(key).validate(isValid)",
    imports = arrayOf("com.example.validate"),
    ),
    )
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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36. Minimal APIs
    › Easier to maintain and change @Deprecated(
    message = "Use a chained .validate {} call instead",
    level = DeprecationLevel.HIDDEN,
    replaceWith = ReplaceWith(
    "this.stringPref(key).validate(isValid)",
    imports = arrayOf("com.example.validate"),
    ),
    )
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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37. Minimal APIs
    › Easier to maintain and change @Deprecated(
    message = "Use a chained .validate {} call instead",
    level = DeprecationLevel.HIDDEN,
    replaceWith = ReplaceWith(
    "this.stringPref(key).validate(isValid)",
    imports = arrayOf("com.example.validate"),
    ),
    )
    public fun Krate.stringPref(
    key: String,
    isValid: (newValue: String) -> Boolean,
    )
    

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38. Minimal APIs
    › Easier to maintain and change
    

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39. Minimal APIs
    › Easier to maintain and change
    › Easier to learn
    

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40. Minimal APIs
    › Easier to maintain and change
    › Easier to learn
    

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41. Minimal APIs
    › Easier to maintain and change
    › Easier to learn
    

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42. Minimal APIs
    › Easier to maintain and change
    › Easier to learn
    › Harder to misuse
    

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43. Planning
    

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44. Planning
    

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45. Planning
    

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46. Planning
    

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47. Visibility in Kotlin
    public
    

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48. Visibility in Kotlin
    public
    private
    

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49. Visibility in Kotlin
    public
    private internal
    

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50. Visibility in Kotlin
    public
    private internal
    

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51. Internal visibility
    public interface Service {
    fun createUser(): User
    }
    internal class NetworkService : Service {
    override fun createUser(): User {
    ...
    }
    }
    

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52. Internal visibility
    public class NetworkClient {
    public var state: State = Disconnected
    internal set
    public fun connect() {
    state = Connected
    }
    }
    

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53. Internal visibility
    internal fun String.asMention(): String = "@$this"
    

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54. Internal visibility
    

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55. Testing
    

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56. Testing
    private var state: State
    

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57. @Test
    fun verifyState() {
    assertEquals(expectedState, state)
    }
    Testing
    private var state: State
    

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58. @Test
    fun verifyState() {
    assertEquals(expectedState, state)
    }
    Testing
    private var state: State
    

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59. @Test
    fun verifyState() {
    assertEquals(expectedState, state)
    }
    Testing
    internal var state: State
    

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60. @Test
    fun verifyState() {
    assertEquals(expectedState, state)
    }
    Testing
    @VisibleForTesting(otherwise = PRIVATE)
    internal var state: State
    

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61. Java interop
    

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62. Java interop
    class Repository {
    internal fun createEntity() { ... }
    }
    

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63. Java interop
    void repositoryExample() {
    }
    class Repository {
    internal fun createEntity() { ... }
    }
    

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64. Java interop
    void repositoryExample() {
    new Repository().createEntity$examplelibrary();
    }
    class Repository {
    internal fun createEntity() { ... }
    }
    

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65. Java interop
    void repositoryExample() {
    new Repository().createEntity$examplelibrary();
    }
    class Repository {
    internal fun createEntity() { ... }
    }
    

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66. class Repository {
    internal fun createEntity() { ... }
    }
    Java interop
    @JvmName("pleaseDoNotCallThisMethod")
    ();
    void repositoryExample() {
    new Repository().
    }
    pleaseDoNotCallThisMethod
    

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67. Java interop
    void repositoryExample() {
    new Repository().
    }
    class Repository {
    internal fun createEntity() { ... }
    }
    Cannot resolve method 'createEntity' in 'Repository'
    @JvmSynthetic
    ();
    createEntity
    

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68. Explicit API mode
    

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69. Explicit API mode
    › Explicit visibility modifiers for all declarations
    

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70. Explicit API mode
    › Explicit visibility modifiers for all declarations
    › Explicit types for public declarations
    

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71. Explicit API mode
    kotlin {
    explicitApi()
    }
    

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72. Explicit API mode
    kotlin {
    explicitApi()
    }
    tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
    kotlinOptions {
    freeCompilerArgs += [
    '-Xexplicit-api=strict',
    ]
    }
    }
    

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73. Explicit API mode
    kotlin {
    explicitApi()
    }
    tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
    kotlinOptions {
    freeCompilerArgs += [
    '-Xexplicit-api=strict',
    '-progressive',
    ]
    }
    }
    

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74. Explicit API mode
    kotlin {
    explicitApiWarning()
    }
    tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
    kotlinOptions {
    freeCompilerArgs += [
    '-Xexplicit-api=warning',
    '-progressive',
    ]
    }
    }
    

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75. Explicit API mode
    class User(var name: String, var age: Int) {
    fun sayHi() {
    println("Hi, I'm $name")
    }
    fun reset() {
    name = ""
    age = 0
    }
    }
    

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76. Explicit API mode
    class User(var name: String, var age: Int) {
    fun sayHi() {
    println("Hi, I'm $name")
    }
    fun reset() {
    name = ""
    age = 0
    }
    }
    

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77. public
    Explicit API mode
    public class User(var name: String, var age: Int) {
    fun sayHi() {
    println("Hi, I'm $name")
    }
    fun reset() {
    name = ""
    age = 0
    }
    }
    

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78. Explicit API mode
    public class User(public var name: String, var age: Int) {
    fun sayHi() {
    println("Hi, I'm $name")
    }
    fun reset() {
    name = ""
    age = 0
    }
    }
    public
    

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79. Explicit API mode
    public class User(public var name: String, public var age: Int) {
    public fun sayHi() {
    println("Hi, I'm $name")
    }
    fun reset() {
    name = ""
    age = 0
    }
    }
    

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80. Explicit API mode
    public class User(public var name: String, public var age: Int) {
    public fun sayHi() {
    println("Hi, I'm $name")
    }
    internal fun reset() {
    name = ""
    age = 0
    }
    }
    

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81. Explicit API mode
    private val DEFAULT_CLIENT = Client()
    public interface ClientFactory {
    public fun client() = DEFAULT_CLIENT
    }
    

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82. Explicit API mode
    private val DEFAULT_CLIENT = Client()
    public interface ClientFactory {
    public fun client() = DEFAULT_CLIENT
    }
    

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83. Explicit API mode
    private val DEFAULT_CLIENT = Client()
    public interface ClientFactory {
    public fun client() = DEFAULT_CLIENT
    }
    

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84. Explicit API mode
    private val DEFAULT_CLIENT = Client()
    public interface ClientFactory {
    public fun client() = DEFAULT_CLIENT
    }
    

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85. Explicit API mode
    private val DEFAULT_CLIENT = OfflineClient()
    public interface ClientFactory {
    public fun client() = DEFAULT_CLIENT
    }
    

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86. Explicit API mode
    private val DEFAULT_CLIENT = OfflineClient()
    public interface ClientFactory {
    public fun client(): Client = DEFAULT_CLIENT
    }
    

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87. Explicit API mode
    › Explicit visibility modifiers for all declarations
    › Explicit types for public declarations
    

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88. Explicit API mode
    › Explicit visibility modifiers for all declarations
    › Explicit types for public declarations
    › Configured per-module
    

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89. Explicit API mode
    › Explicit visibility modifiers for all declarations
    › Explicit types for public declarations
    › Configured per-module
    › Strict or warning level
    

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90. Published API
    

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91. Published API
    public inline fun song() {
    secretFunction()
    }
    internal fun secretFunction() {
    println("through the mountains")
    }
    

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92. Published API
    public inline fun song() {
    secretFunction()
    }
    internal fun secretFunction() {
    println("through the mountains")
    }
    fun clientCode() {
    song()
    }
    

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93. fun clientCode() {
    }
    secretFunction()
    Published API
    public inline fun song() {
    secretFunction()
    }
    internal fun secretFunction() {
    println("through the mountains")
    }
    e: Public-API inline function cannot access non-public-API
    song()
    

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94. Published API
    public inline fun song() {
    secretFunction()
    }
    internal fun secretFunction() {
    println("through the mountains")
    }
    fun clientCode() {
    }
    secretFunction()
    

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95. Published API
    fun clientCode() {
    }
    secretFunction()
    public inline fun song() {
    secretFunction()
    }
    internal fun secretFunction() {
    println("through the mountains")
    }
    

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96. Published API
    fun clientCode() {
    }
    song()
    @PublishedApi
    public inline fun song() {
    secretFunction()
    }
    internal fun secretFunction() {
    println("through the mountains")
    }
    

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97. Published API
    fun clientCode() {
    song()
    secretFunction()
    }
    public inline fun song() {
    secretFunction()
    }
    @PublishedApi
    internal fun secretFunction() {
    println("through the mountains")
    }
    e: Cannot access 'secretFunction': it is internal
    

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98. Published API
    fun clientCode() {
    }
    song()
    @PublishedApi
    public inline fun song() {
    secretFunction()
    }
    internal fun secretFunction() {
    println("through the mountains")
    }
    

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100. Opt-in APIs
     core
     

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101. Opt-in APIs
     core
     addon
     

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102. Opt-in APIs
     core
     addon
     

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103. core
     addon
     Opt-in APIs
     

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104. core
     addon
     Opt-in APIs
     

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105. package com.example.lib.core
     public annotation class InternalMyLibraryApi
     core
     addon
     Opt-in APIs
     

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106. Opt-in APIs
     package com.example.lib.core
     public annotation class InternalMyLibraryApi
     

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107. Opt-in APIs
     package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.ERROR,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     

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108. Opt-in APIs
     package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.WARNING,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     

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109. Opt-in APIs
     package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.ERROR,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     

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110. Opt-in APIs
     package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.ERROR,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=kotlin.RequiresOptIn',
     ]
     }
     }
     

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111. Opt-in APIs
     package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.ERROR,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=kotlin.RequiresOptIn',
     ]
     }
     }
     

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112. Opt-in APIs
     package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.ERROR,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=kotlin.RequiresOptIn',
     ]
     }
     }
     

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113. Opt-in APIs
     package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.ERROR,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     @InternalMyLibraryApi
     public fun coreApi()
     

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114. package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.ERROR,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     @InternalMyLibraryApi
     public fun coreApi()
     core
     addon
     Opt-in APIs
     

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115. public fun addonFunction() {
     coreApi()
     }
     package com.example.lib.core
     @RequiresOptIn(
     level = RequiresOptIn.Level.ERROR,
     message = "This is internal API for my library, " +
     "please don't rely on it."
     )
     public annotation class InternalMyLibraryApi
     @InternalMyLibraryApi
     public fun coreApi()
     core
     addon
     Opt-in APIs
     

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116. core
     addon
     @InternalMyLibraryApi
     public fun coreApi()
     Opting in
     public fun addonFunction() {
     coreApi()
     }
     

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117. Opting in
     @InternalMyLibraryApi
     public fun coreApi()
     @InternalMyLibraryApi
     public fun addonFunction() {
     coreApi()
     }
     

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118. Opting in
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=com.example.lib.core.InternalMyLibraryApi',
     ]
     }
     }
     @InternalMyLibraryApi
     public fun coreApi()
     public fun addonFunction() {
     coreApi()
     }
     @InternalMyLibraryApi
     

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119. Opting in
     @InternalMyLibraryApi
     public fun coreApi()
     public fun addonFunction() {
     coreApi()
     }
     

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120. Opting in
     @InternalMyLibraryApi
     public fun coreApi()
     public fun addonFunction() {
     @OptIn(InternalMyLibraryApi::class)
     coreApi()
     }
     

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121. Opting in
     @InternalMyLibraryApi
     public fun coreApi()
     public fun addonFunction() {
     @OptIn(InternalMyLibraryApi::class)
     coreApi()
     }
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=kotlin.RequiresOptIn',
     ]
     }
     }
     

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122. Opting in
     @InternalMyLibraryApi
     public fun coreApi()
     public fun addonFunction() {
     @OptIn(InternalMyLibraryApi::class)
     coreApi()
     }
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=kotlin.RequiresOptIn',
     ]
     }
     }
     

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123. Opting in
     @InternalMyLibraryApi
     public fun coreApi()
     public fun addonFunction() {
     @OptIn(InternalMyLibraryApi::class)
     coreApi()
     }
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=kotlin.RequiresOptIn',
     ]
     }
     }
     

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124. Opting in
     @InternalMyLibraryApi
     public fun coreApi()
     @OptIn(InternalMyLibraryApi::class)
     public fun addonFunction() {
     coreApi()
     }
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=kotlin.RequiresOptIn',
     ]
     }
     }
     

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125. Opting in
     @InternalMyLibraryApi
     @JvmSynthetic
     public fun coreApi()
     @OptIn(InternalMyLibraryApi::class)
     public fun addonFunction() {
     coreApi()
     }
     tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
     freeCompilerArgs += [
     '-Xopt-in=kotlin.RequiresOptIn',
     ]
     }
     }
     

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126. Opt-in conventions
     InternalCoroutinesApi
     DelicateCoroutinesApi
     ExperimentalCoroutinesApi
     ObsoleteCoroutinesApi
     

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127. Android time
     

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128. Android time
     

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129. Android time
     implementation 'androidx.annotation:annotation:1.1.0'
     

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130. Android time
     implementation 'androidx.annotation:annotation-experimental:1.1.0'
     

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131. core
     Validating API
     

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132. core
     Validating API
     buildscript {
     dependencies {
     classpath 'org.jetbrains.kotlinx:binary-compatibility-validator:0.5.0'
     }
     }
     apply plugin: 'binary-compatibility-validator'
     

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133. core
     apiValidation {
     ignoredPackages += [
     'com/getstream/sdk/chat/databinding',
     'io/getstream/chat/android/ui/databinding',
     ]
     ignoredProjects += [
     'stream-chat-android-docs',
     'stream-chat-android-sample',
     'stream-chat-android-ui-components-sample',
     'stream-chat-android-test',
     ]
     nonPublicMarkers += [
     'io.getstream.chat.android.core.internal.InternalStreamChatApi',
     ]
     }
     Validating API
     

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134. core
     apiValidation {
     ignoredPackages += [
     'com/getstream/sdk/chat/databinding',
     'io/getstream/chat/android/ui/databinding',
     ]
     ignoredProjects += [
     'stream-chat-android-docs',
     'stream-chat-android-sample',
     'stream-chat-android-ui-components-sample',
     'stream-chat-android-test',
     ]
     nonPublicMarkers += [
     'io.getstream.chat.android.core.internal.InternalStreamChatApi',
     ]
     }
     Validating API
     

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135. core
     apiValidation {
     ignoredPackages += [
     'com/getstream/sdk/chat/databinding',
     'io/getstream/chat/android/ui/databinding',
     ]
     ignoredProjects += [
     'stream-chat-android-docs',
     'stream-chat-android-sample',
     'stream-chat-android-ui-components-sample',
     'stream-chat-android-test',
     ]
     nonPublicMarkers += [
     'io.getstream.chat.android.core.internal.InternalStreamChatApi',
     ]
     }
     Validating API
     

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136. core
     apiValidation {
     ignoredPackages += [
     'com/getstream/sdk/chat/databinding',
     'io/getstream/chat/android/ui/databinding',
     ]
     ignoredProjects += [
     'stream-chat-android-docs',
     'stream-chat-android-sample',
     'stream-chat-android-ui-components-sample',
     'stream-chat-android-test',
     ]
     nonPublicMarkers += [
     'io.getstream.chat.android.core.internal.InternalStreamChatApi',
     ]
     }
     Validating API
     

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137. core
     Validating API gradlew apiDump
     

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138. core
     Validating API
     public abstract interface class io/getstream/chat/android/client/ChatEventListener {
     public abstract fun onEvent (Lio/getstream/chat/android/client/events/ChatEvent;)V
     }
     public final class io/getstream/chat/android/client/api/models/AutocompleteFilterObject :
     io/getstream/chat/android/client/api/models/FilterObject {
     public final fun component1 ()Ljava/lang/String;
     public final fun component2 ()Ljava/lang/String;
     public final fun copy
     (Ljava/lang/String;Ljava/lang/String;)Lio/getstream/chat/android/client/api/models/Autocompl
     eteFilterObject;
     public fun equals (Ljava/lang/Object;)Z
     public final fun getFieldName ()Ljava/lang/String;
     public final fun getValue ()Ljava/lang/String;
     public fun hashCode ()I
     public fun toString ()Ljava/lang/String;
     }
     gradlew apiDump
     

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139. core
     Validating API gradlew apiCheck
     

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140. core
     Validating API
     Execution failed for task ':stream-chat-android-client:apiCheck'.
     > API check failed for project stream-chat-android-client.
     @@ -218,9 +218,8 @@
     public final class io/getstream/chat/android/client/api/models/AutocompleteFilterObject :
     io/getstream/chat/android/client/api/models/FilterObject {
     public final fun component1 ()Ljava/lang/String;
     - public final fun component2 ()Ljava/lang/String;
     - public final fun copy
     (Ljava/lang/String;Ljava/lang/String;)Lio/getstream/chat/android/client/api/models/Autocompl
     eteFilterObject;
     + public final fun copy
     (Ljava/lang/String;)Lio/getstream/chat/android/client/api/models/AutocompleteFilterObject;
     public fun equals (Ljava/lang/Object;)Z
     public final fun getFieldName ()Ljava/lang/String;
     public final fun getValue ()Ljava/lang/String;
     You can run :stream-chat-android-client:apiDump task to overwrite API declarations
     gradlew apiCheck
     

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141. core
     Validating API
     Execution failed for task ':stream-chat-android-client:apiCheck'.
     > API check failed for project stream-chat-android-client.
     @@ -218,9 +218,8 @@
     public final class io/getstream/chat/android/client/api/models/AutocompleteFilterObject :
     io/getstream/chat/android/client/api/models/FilterObject {
     public final fun component1 ()Ljava/lang/String;
     - public final fun component2 ()Ljava/lang/String;
     - public final fun copy
     (Ljava/lang/String;Ljava/lang/String;)Lio/getstream/chat/android/client/api/models/Autocompl
     eteFilterObject;
     + public final fun copy
     (Ljava/lang/String;)Lio/getstream/chat/android/client/api/models/AutocompleteFilterObject;
     public fun equals (Ljava/lang/Object;)Z
     public final fun getFieldName ()Ljava/lang/String;
     public final fun getValue ()Ljava/lang/String;
     You can run :stream-chat-android-client:apiDump task to overwrite API declarations
     gradlew apiCheck
     

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142. core
     Validating API
     Execution failed for task ':stream-chat-android-client:apiCheck'.
     > API check failed for project stream-chat-android-client.
     @@ -218,9 +218,8 @@
     public final class io/getstream/chat/android/client/api/models/AutocompleteFilterObject :
     io/getstream/chat/android/client/api/models/FilterObject {
     public final fun component1 ()Ljava/lang/String;
     - public final fun component2 ()Ljava/lang/String;
     - public final fun copy
     (Ljava/lang/String;Ljava/lang/String;)Lio/getstream/chat/android/client/api/models/Autocompl
     eteFilterObject;
     + public final fun copy
     (Ljava/lang/String;)Lio/getstream/chat/android/client/api/models/AutocompleteFilterObject;
     public fun equals (Ljava/lang/Object;)Z
     public final fun getFieldName ()Ljava/lang/String;
     public final fun getValue ()Ljava/lang/String;
     You can run :stream-chat-android-client:apiDump task to overwrite API declarations
     gradlew apiCheck
     

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143. core
     Validating API
     

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144. • Mastering API Visibility in Kotlin
      https://zsmb.co/mastering-api-visibility-in-kotlin/
     • Maintaining Compatibility in Kotlin Libraries
      https://zsmb.co/maintaining-compatibility-in-kotlin-libraries/
     • How to Build Awesome Android Libraries
      https://zsmb.co/talks/how-to-build-awesome-android-libraries/
     • Effective Java, 3rd Edition
      https://www.amazon.com/Effective-Java-Joshua-Bloch/dp/0134685997
     • Effective Kotlin
      https://leanpub.com/effectivekotlin/
     Resources
     

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145. zsmb13
     zsmb.co/talks
     

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146. Mastering API
     Visibility in Kotlin
     zsmb.co/talks
     zsmb13
     Márton Braun
     › Minimal API is nice
     › Internal visibility
     › Explicit API mode
     › Published API
     › Opt-in APIs
     

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