Refactoring Legacy Code with Kotlin and Coroutines

by Ash Davies
presented on August 30, 2019 @Kotlin/Everywhere Hamburg

Transcript

1. Refactoring Legacy Code with Kotlin & Coroutines Kotlin Everywhere: Hamburg @askashdavies
2. @askashdavies
3. Java @askashdavies
4. { } @askashdavies
5. Streams ↝ @askashdavies
6. @askashdavies
7. Kotlin @askashdavies
8. Null @askashdavies
9. if (foo == null) { bar(); } @askashdavies
10. O"ensive Code < > @askashdavies
11. Urgency @askashdavies
12. Kotlin? @askashdavies
13. Kotlin @askashdavies
14. @askashdavies
15. Google IO 2018 @askashdavies
16. ! " @askashdavies
17. Google IO 2019 @askashdavies
18. Kotlin @askashdavies
19. Libraries @askashdavies
20. @askashdavies
21. @askashdavies
22. @askashdavies
23. @askashdavies
24. @askashdavies
25. @askashdavies
26. Kotlin @askashdavies
27. Idiomacy @askashdavies
28. @askashdavies
29. Idiomatic Code @askashdavies
30. Idiomatic Code • Consistent, easier to read • Less cognitive load • Less ambiguity • Function > Style @askashdavies
31. Code Style • kotlinlang.org/docs/reference/coding-conventions.html • android.github.io/kotlin-guides/style.html @askashdavies
32. Refactoring Legacy Code @askashdavies
33. ⌃⌥⇧K @askashdavies
34. @askashdavies
35. @askashdavies
36. public class BadJavaActivity extends Activity { @Inject Dependency dependency; } @askashdavies
37. General Assumptions @askashdavies
38. class BadKotlinActivity : Activity() { @Inject var dependency: Dependency? = null } @askashdavies
39. class SlightlyLessBadKotlinActivity : Activity() { @Inject internal lateinit var dependency: Dependency } @askashdavies
40. UninitializedPrope.yAccessException! @askashdavies
41. lateinit var file: File if (::file.isInitialized) { /* ... */ } @askashdavies
42. Data Classes @askashdavies
43. public class User { private String firstName; private String lastName; public User(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } @Override public boolean equals(Object o) { if (this == o) { return true; } if (o == null || getClass() != o.getClass()) { return false; } User user = (User) o; return Objects.equals(firstName, user.firstName) && Objects.equals(lastName, user.lastName); } @Override public int hashCode() { return Objects.hash(firstName, lastName); } } @askashdavies
44. class User(var firstName: String?, var lastName: String?) { override fun equals(o: Any?): Boolean { if (this === o) { return true } if (o == null || javaClass != o.javaClass) { return false } val user = o as User? return firstName == user!!.firstName && lastName == user.lastName } override fun hashCode(): Int { return Objects.hash(firstName, lastName) } } @askashdavies
45. data class User(val firstName: String, val lastName: String) @askashdavies
46. data class User(val firstName: String, val lastName: String? = null) @askashdavies
47. @NotNull public final User copy(@Nullable String firstName, @Nullable String lastName) { return new User(firstName, lastName); } @askashdavies
48. Kotlin • Singleton objects • String interpolation • Elvis operator ! • Destructuring • Extension functions • Scoping functions @askashdavies
49. Maintaining History @askashdavies
50. Maintaining History • Change extension .java -> .kt • First commit • Apply Kotlin conversion • Second commit @askashdavies
51. Maintaining History Refactoring @askashdavies
52. Refactoring @askashdavies
53. Refactoring SOLID • Single-responsibility • Open-closed • Liskov substitution • Interface segregation • Dependency inversion @askashdavies
54. Refactoring Single Responsibility @askashdavies
55. Perspective @askashdavies
56. Asynchronicity @askashdavies
57. Concurrency is Hard @askashdavies
58. Thread new Thread(() -> { foo(); }).start(); @askashdavies
59. CompletableFuture CompletableFuture.supplyAsync(this::findSomeData) .thenApply(this:: intReturningMethod) .thenAccept(this::notify); @askashdavies
60. RxJava Observable .fromIterable(resourceDraft.getResources()) .flatMap(resourceServiceApiClient::createUploadContainer) .zipWith(Observable.fromIterable(resourceDraft.getResources()), Pair::create) .flatMap(uploadResources()) .toList() .toObservable() .flatMapMaybe(resourceCache.getResourceCachedItem()) .defaultIfEmpty(Resource.getDefaultItem()) .flatMap(postResource(resourceId, resourceDraft.getText(), currentUser, resourceDraft.getIntent())) .observeOn(AndroidSchedulers.mainThread()) .subscribeOn(Schedulers.io()) .subscribe( resource -> repository.setResource(resourceId, resource, provisionalResourceId), resourceUploadError(resourceId, resourceDraft, provisionalResourceId) ); @askashdavies
61. @askashdavies
62. What If? @askashdavies
63. Coroutines @askashdavies
64. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
65. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
66. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
67. ⚖ Stability @askashdavies
68. @askashdavies
69. @Annotations ( ! Here be dragons) @askashdavies
70. Annotations @ExperimentalCoroutinesApi // ⚠ @askashdavies
71. Annotations @ExperimentalCoroutinesApi // ⚠ @FlowPreview // ⚠ @askashdavies
72. Annotations @ExperimentalCoroutinesApi // ⚠ @FlowPreview // ⚠ @ObsoleteCoroutinesApi // ⚠ @askashdavies
73. Annotations @ExperimentalCoroutinesApi // ⚠ @FlowPreview // ⚠ @ObsoleteCoroutinesApi // ⚠ @InternalCoroutinesApi // ☠ @askashdavies
74. Annotations @Experimental @askashdavies
75. ! Coroutines @askashdavies
76. ! Native (rst-pa-y library @askashdavies
77. E"cient @askashdavies
78. ! Easy-to-use @askashdavies
79. ! suspend fun @askashdavies
80. ! Suspend fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
81. ! Suspend fun main() { GlobalScope.launch { doWorld() println("Hello,") Thread.sleep(2000L) } } suspend fun doWorld() { delay(1000L) println("World!") } // Hello, // World! @askashdavies
82. ! Suspend fun main() { GlobalScope.launch { doWorld() println("Hello,") Thread.sleep(2000L) } } suspend fun doWorld() { withContext(Dispatchers.IO) { delay(1000L) println("World!") } } // Hello, // World! @askashdavies
83. Dispatchers @askashdavies
84. Dispatchers • Default • IO • Main • Android (Main Thread Dispatcher) • JavaFx (Application Thread Dispatcher) • Swing (Event Dispatcher Thread) • Unconfined @askashdavies
85. Testing @Test fun testFoo() = runBlockingTest { val actual = foo() // ... } suspend fun foo() { delay(1_000) // ... } @askashdavies
86. Fu#her Reading • Google Codelab: Refactoring to Kotlin https://codelabs.developers.google.com/codelabs/java-to-kotlin/ • KotlinX Coroutine Test https://github.com/Kotlin/kotlinx.coroutines/tree/master/kotlinx-coroutines-test • Sean McQuillan: Coroutines + Testing = https://www.droidcon.com/media-detail?video=352671106 • Ash Davies: RxJava & Coroutines: A Practical Analysis v3 https://speakerdeck.com/ashdavies/rxjava-and-coroutines-a-practical-analysis- v3 @askashdavies
87. Thanks! @askashdavies