ContractsでCompilerを賢くしよう / love_kotlin #5

Transcript

1. Contractsで Compilerを賢くしよう Kotlin愛好会 vol5
2. About me •Kenji Abe •Cookpad Inc. •Android Developer •Twitter: @STAR_ZERO
3. Contracts •Kotlin 1.3の新機能 •関数の動作を明示的にCompilerへ伝える •スマートキャストをより便利に
4. 今回の環境 •IntelliJ IDEA 2018.2.5 •Kotlin 1.3.0-rc-190
5. 簡単な例
6. Contractsなし fun isNonNull(s: String?): Boolean { return s != null } fun hoge(s: String?) { if (isNonNull(s)) { // Smart CastされないのでCompile Error println(s.length) } }
7. Contractsあり @ExperimentalContracts fun isNonNull(s: String?): Boolean { contract { returns(true) implies (s != null) } return s != null }
8. Contractsあり @ExperimentalContracts fun hoge(s: String?) { if (isNonNull(s)) { // Smart Castしてくれる println(s.length) } }
9. Contractsなし fun runFunc(func: () -> Unit) { func() } fun hoge() { var x: Int runFunc { x = 10 } // Variable 'x' must be initialized println(x) }
10. Contractsあり @ExperimentalContracts fun runFunc(func: () -> Unit) { contract { callsInPlace(func, InvocationKind.EXACTLY_ONCE) } func() }
11. Contractsあり @ExperimentalContracts fun hoge() { var x: Int runFunc { x = 10 } // エラーなし println(x) }
12. returns - implies
13. returns - implies @ExperimentalContracts fun isNonNull(s: String?): Boolean { contract { returns(true) implies (s != null) } return s != null } •戻り値によって決まる引数またはthisの状態を定義
14. returns - implies •returns() •returns(value: Any?) ‣ true, false, null •returnsNotNull()
15. returns - implies •implies ‣ == null, != null ‣ is, !is
16. Example 1 @ExperimentalContracts fun validate(s: String?) { contract { returns() implies (s != null) } if (s.isNullOrEmpty()) { throw IllegalArgumentException() } }
17. Example 1 @ExperimentalContracts fun hoge(value: String?) { validate(value) println("length = ${value.length}") }
18. Example 2 @ExperimentalContracts fun isString(v: Any?): Boolean { contract { returns(true) implies (v is String) } return v is String }
19. Example 2 @ExperimentalContracts fun hoge(v: Any?) { if (isString(v)) { println("length = ${v.length}") } }
20. Example 3 @ExperimentalContracts fun castInt(v: Any?): Int? { contract { returnsNotNull() implies (v is Int) } return v as? Int }
21. Example 3 @ExperimentalContracts fun hoge(v: Any?) { if (castInt(v) != null) { println("${v + v}") } }
22. Example 4 @ExperimentalContracts fun Any?.isString(): Boolean { contract { returns(true) implies (this@isString is String) } return this is String }
23. Example 4 @ExperimentalContracts fun hoge(v: Any?) { if (v.isString()) { println("length = ${v.length}") } }
24. Example 5 @ExperimentalContracts fun stringOrInt(v: Any?) : Boolean { contract { returns(true) implies (v is String) returns(false) implies (v is Int) } return v is String }
25. Example 5 @ExperimentalContracts fun hoge(v: Any?) { if (stringOrInt(v)) { println("length = ${v.length}") } else { println("plus = ${1 + v}") } }
26. callsInPlace
27. callsInPlace @ExperimentalContracts fun runFunc(func: () -> Unit) { contract { callsInPlace(func, InvocationKind.EXACTLY_ONCE) } func() } •引数の関数が何回実行されるか
28. callsInPlace •AT_MOST_ONCE ‣ 1回実行されるか、呼び出されない •AT_LEAST_ONCE ‣ 1回以上呼び出される •EXACTLY_ONCE ‣ 1回だけ呼び出される •UNKNOWN ‣ 呼び出される回数が不明
29. Example 1 @ExperimentalContracts fun runAtLeastOnce(func: () -> Unit) { contract { callsInPlace(func, InvocationKind.AT_LEAST_ONCE) } func() }
30. Example 1 @ExperimentalContracts fun hoge() { var x: Int runAtLeastOnce { x = 10 } println(x) }
31. Example 2 @ExperimentalContracts fun runAtMostOnce(func: () -> Unit) { contract { callsInPlace(func, InvocationKind.AT_MOST_ONCE) } func() }
32. Example 2 @ExperimentalContracts fun hoge() { var x: Int runAtMostOnce { x = 10 } // Variable 'x' must be initialized println(x) }
33. Example 3 @ExperimentalContracts fun runFuncs(func1: () -> Unit, func2: () -> Unit) { contract { // func1だけ設定 callsInPlace(func1, InvocationKind.EXACTLY_ONCE) } func1() func2() }
34. Example 3 @ExperimentalContracts fun hoge() { var x: Int runFuncs({ x = 10 }) { x = 20 } // Variable 'x' must be initialized println(x) }
35. Example 4 @ExperimentalContracts fun runFuncs(func1: () -> Unit, func2: () -> Unit) { contract { // 今度はfunc2だけ設定 callsInPlace(func2, InvocationKind.EXACTLY_ONCE) } func1() func2() }
36. Example 4 @ExperimentalContracts fun hoge() { var x: Int runFuncs({ x = 10 }) { x = 20 } println(x) }
37. Example 5 @ExperimentalContracts fun runFunc(func: () -> Unit) { contract { callsInPlace(func, InvocationKind.EXACTLY_ONCE) } func() }
38. Example 5 @ExperimentalContracts fun hoge() { var x: Int runFunc({ x = 10 }) // <- 括弧で括る // Variable 'x' must be initialized println(x) }
39. Example 6 @ExperimentalContracts fun complex(v: Any?, func: () -> Unit): Boolean { contract { returns(true) implies (v is String) callsInPlace(func, InvocationKind.EXACTLY_ONCE) } func() return v is String }
40. Example 6 @ExperimentalContracts fun hoge(v: Any) { var x: Int if (complex(v) { x = 10 }) { println("length = ${v.length}") } println("x = $x") }
41. 注意
42. 注意 class Helper { @ExperimentalContracts fun isNonNull(s: String?): Boolean { // Contracts are allowed only for top-level functions contract { returns(true) implies (s != null) } return s != null } } •Top-Level関数でしか使えない
43. まとめ
44. まとめ •Contractsを使うとComplierがちょっと賢くなる •拡張関数で使うのが現実的な気がする •今後に期待？
45. ありがとうございました