Generating Kotlin extension functions for Annotation Processing

Presented:
* 27th of October 2018 - DevFest Wrocław 2018, Poland
* 5th of April 2019 - Droidcon Italy 2019
* 11th of April 2019 - Toast Wrocław #23

Transcript

1. @blipinsk Fabulous Generating Kotlin extension functions for Annotation Processing Ba#ek Lipiński @blipinsk
2. @blipinsk Compiler Annotations @ExampleAnnotation
3. @blipinsk Annotations @ExampleAnnotation light can be included in codebase Labels for marking code
4. @blipinsk Compiler (CAN BE) HEAVY should never be included in codebase looks for uses of Annotations CAN GENERATE CODE!
5. @blipinsk Annotation processors cannot modify exisiting code. They can only generate new code.
6. @blipinsk Generated Code Annotations Compiler compile time UNKNOWN until Generated (DUH!)
7. @blipinsk compile time only new code unknown until generated compile time only new code unknown until generated WHAT WILL BE GENERATED? WHEN WILL IT BE GENERATED?
8. @blipinsk compile time only new code unknown until generated + + di>cult to refer to generated code =
9. @blipinsk “I don’t care” approach “ReDection bridge” approach
10. @blipinsk “I don’t care” approach Dagger 2 dependency injection framework generates a lot of code one entry point to the generated code (class that implements your component) Dagger<Component>
11. @blipinsk “I don’t care” approach // … import com.bartoszlipinski.example.DaggerAppComponent class ExampleApplication : Application() { private val component: AppComponent by lazy { DaggerAppComponent .builder() .appModule(AppModule(this)) .build() } override fun onCreate() { super.onCreate() component.inject(this) } }
12. @blipinsk “I don’t care” approach // … import com.bartoszlipinski.example.DaggerAppComponent class ExampleApplication : Application() { private val component: AppComponent by lazy { DaggerAppComponent .builder() .appModule(AppModule(this)) .build() } override fun onCreate() { super.onCreate() component.inject(this) } } Dagger will give you this class in COMPILE-TIME (if everything goes correctly)
13. @blipinsk “I don’t care” approach • easy to implement (for the developer of the library) • not straighforward • strongly depends on documentation • puts responsibility on the user of the library
14. @blipinsk “ReDection bridge” approach Compiler Library Re2ection bridge compile time Generated Code knows how compiler works
15. @blipinsk “ReDection bridge” approach Compiler Library Re2ection bridge compile time Generated Code runtime using Java Reflection
16. @blipinsk “ReDection bridge” approach BuJerKnife reduces Android boilerplate code (for views, resources, etc.) generates _ViewBinding classes available through ButterKnife.bind(…)
17. @blipinsk “ReDection bridge” approach // Generated code from Butter Knife. Do not modify! package com.barteklipinski.sample; // imports … public final class MainActivity_ViewBinding implements Unbinder { // … class contents } Re2ection bridge
18. @blipinsk “ReDection bridge” approach // Generated code from Butter Knife. Do not modify! package com.barteklipinski.sample; // imports … public final class MainActivity_ViewBinding implements Unbinder { // … class contents } Re2ection bridge
19. @blipinsk “ReDection bridge” approach // Generated code from Butter Knife. Do not modify! package com.barteklipinski.sample; // imports … public final class MainActivity_ViewBinding implements Unbinder { // … class contents } Re2ection bridge
20. @blipinsk “ReDection bridge” approach // Generated code from Butter Knife. Do not modify! package com.barteklipinski.sample; // imports … public final class MainActivity_ViewBinding implements Unbinder { // … class contents } Re2ection bridge
21. @blipinsk • @nd generated classes • create instances of them • return those instances in a form of the Unbinder inteBace “ReDection bridge” approach val unbinder : Unbinder = ButterKnife.bind(target) Re2ection bridge
22. @blipinsk • straighforward • puts responsibility on the developer of the library (not user) • depends on Java ReEection (some peBormance overhead) “ReDection bridge” approach
23. @blipinsk “I don’t care” approach “ReDection bridge” approach
24. @blipinsk “I don’t care” approach “ReDection bridge” approach “Extension bridge” approach
25. @blipinsk “Extension bridge” approach Compiler Library Extension bridge “End Cap” compile time Generated Code PRETENDS TO BE REAL
26. @blipinsk “Extension bridge” approach Compiler Library Extension bridge “End Cap” compile time Generated Code Extension bridge “Core” knows how compiler works PRETENDS TO BE REAL
27. @blipinsk “Extension bridge” approach Compiler Library Extension bridge “End Cap” compile time Generated Code runtime Extension bridge “Core” NOT using* Java Reflection
28. @blipinsk Why Extension bridge? Kotlin extension functions!
29. @blipinsk Why Kotlin extension functions? Annotation processors cannot modify exisiting code. They can only generate new code. fun String.toUpperCamelCase(): String { // convert… } add* behaviour to existing classes (without modifying them) "DROIDcon ItAly".toUpperCamelCase() // == “DroidconItaly” Receiver Type
30. @blipinsk “Extension bridge” proof of concept libraries Dagger 2 ! BuRerKnife ! h9ps://github.com/blipinsk/dagger2-ktx h9ps://github.com/blipinsk/bu9erknife-ktx
31. @blipinsk fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
32. @blipinsk fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
33. @blipinsk fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
34. @blipinsk fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
35. @blipinsk fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
36. @blipinsk fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library NON-SPECIFIC
37. @blipinsk fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
38. @blipinsk fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
39. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
40. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library MUCH MORE SPECIFIC
41. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
42. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
43. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
44. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
45. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
46. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library ORIGINALLY ACHIEVED WITH JAVA REFLECTION
47. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
48. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
49. @blipinsk object ButterKnifeKtx @UiThread fun ButterKnifeKtx.bind(target: Activity): Unbinder {…} @UiThread fun ButterKnifeKtx.bind(target: View): Unbinder {…} @UiThread fun ButterKnifeKtx.bind(target: Dialog): Unbinder {…} @UiThread fun ButterKnifeKtx.bind(target: Any, source: Activity): Unbinder {…} @UiThread fun ButterKnifeKtx.bind(target: Any, source: View): Unbinder {…} @UiThread fun ButterKnifeKtx.bind(target: Any, source: Dialog): Unbinder {…} BuRerKnife “Extension bridge” proof of concept Extension bridge “End Cap” Artificial object declaration (singleton)
50. @blipinsk BuRerKnife “Extension bridge” proof of concept ButterKnife.bind(this)
51. @blipinsk BuRerKnife “Extension bridge” proof of concept ButterKnifeKtx.bind(this)
52. @blipinsk BuRerKnife “Extension bridge” proof of concept demo
53. @blipinsk Dagger 2 “Extension bridge” proof of concept object Dagger fun <T : Any> Dagger.create(clazz: KClass<T>): T { throw IllegalStateException() } fun Dagger.create(clazz: KClass<AppComponent>): AppComponent { return DaggerAppComponent.create() } Extension bridge “End Cap” shipped as library Extension bridge “Core” generated DaggerAppComponent.create() Dagger.create(AppComponent::class)
54. @blipinsk Dagger 2 “Extension bridge” proof of concept object Dagger fun <T : Any> Dagger.create(clazz: KClass<T>): T { throw IllegalStateException() } fun Dagger.create(clazz: KClass<AppComponent>): AppComponent { return DaggerAppComponent.create() } Extension bridge “End Cap” shipped as library Extension bridge “Core” generated DaggerAppComponent.create() Dagger.create(AppComponent::class)
55. @blipinsk Dagger 2 “Extension bridge” proof of concept object Dagger fun <T : Any> Dagger.create(clazz: KClass<T>): T { throw IllegalStateException() } fun Dagger.create(clazz: KClass<AppComponent>): AppComponent { return DaggerAppComponent.create() } DaggerAppComponent.create() Dagger.create(AppComponent::class) Extension bridge “End Cap” shipped as library Extension bridge “Core” generated
56. @blipinsk “Extension bridge”- how? FunSpec.builder("bind") .returns(ClassName("butterknife", "Unbinder")) .receiver(ClassName("com.bartoszlipinski.butterknifektx", "ButterKnifeKtx")) .addParameter("target", targetClassName) .addStatement("return %T(%L, %L)", initializedClassName, "target", "target") .build() dependencies { implementation ‘com.squareup:kotlinpoet:{version}’ }
57. @blipinsk • straighforward • puts responsibility on the developer of the library (not user) • does NOT depend on Java ReEection* “Extension bridge” approach
58. @blipinsk more demos? “Extension bridge” approach
59. @blipinsk hybrid “Extension bridge” approach Compiler Library Extension bridge “End Cap” compile time Generated Code Extension bridge “Core”
60. @blipinsk hybrid “Extension bridge” approach Compiler Library Extension bridge “End Cap” compile time Generated Code runtime Extension bridge “Core”
61. @blipinsk hybrid “Extension bridge” approach Compiler Library Extension bridge “End Cap” compile time Generated Code runtime Extension bridge “Core” USING Java Reflection
62. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library BuRerKnife hybrid “Extension bridge”
63. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { throw IllegalStateException() } BuRerKnife hybrid “Extension bridge” Extension bridge “End Cap” Extension bridge “Core” generated shipped as library
64. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { return ButterKnife.bind(target) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library BuRerKnife hybrid “Extension bridge”
65. @blipinsk fun ButterKnifeKtx.bind(target: MainActivity): Unbinder { val sourceView = target.getWindow().getDecorView() return MainActivity_ViewBinding(target, sourceView) } fun ButterKnifeKtx.bind(target: Activity): Unbinder { return ButterKnife.bind(target) } Extension bridge “End Cap” Extension bridge “Core” generated shipped as library BuRerKnife hybrid “Extension bridge”
66. @blipinsk Fabulous (psst… we’re hiring!) Thanks! Ba#ek Lipiński @blipinsk