Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
ContractsでCompilerを賢くしよう / love_kotlin #5
Search
star_zero
October 24, 2018
Programming
2
570
ContractsでCompilerを賢くしよう / love_kotlin #5
star_zero
October 24, 2018
Tweet
Share
More Decks by star_zero
See All by star_zero
Jetpack Compose の Side-effect を使いこなす / DroidKaigi 2023
star_zero
4
3.8k
Android 14 新機能 / Android 14 Meetup Nagoya
star_zero
1
480
Android 14 と Predictive back gesture / Shibuya.apk #42
star_zero
0
280
Coroutines Test 入門 / Android Test Night #8
star_zero
2
690
What's new in Jetpack / I/O Extended Japan 2022
star_zero
1
560
Kotlin 2021 Recap / DevFest 2021
star_zero
3
1.2k
Kotlin Symbol Processing (KSP) を使ったコード生成 / DroidKaigi 2021
star_zero
2
4.9k
What's new Android 12
star_zero
0
510
これからはじめるAndroid開発 / DevFest 2020
star_zero
4
670
Other Decks in Programming
See All in Programming
Introduction for Open Source Swift Workshop
giginet
PRO
0
290
Prepare for Jakarta EE 11 - Performance and Developer Productivity
ivargrimstad
0
510
Swiftの型推論を学ぼう | Let's Learn About Type Inference in Swift
omochi
2
660
クソコード動画『カプセル化 Mk-II』 で考える 上手くカプセル化できない理由 / encapsulation2
minodriven
11
8k
Enhancing Applications with Accessibility API
kishikawakatsumi
3
1k
どうしてこうなった命名集 ~🔥編~ / OOC 2024 LT
pictiny
4
2.9k
ファイル先頭の use の意味、説明できますか? 〜PHP の namespace と autoloading の関係を正しく理解しよう〜 / namespace and autoloading in php
okashoi
2
470
Honoとhtmx
yusukebe
6
1.2k
オブジェクト指向は必要なのか / Is object-oriented needed?
kishida
27
19k
「コンパイル時のユニットテスト」導入するとユニットテストを 書かなくてよくなるのか?
tomohisa
9
2.2k
オブジェクトしこう
okuramasafumi
2
130
WinUI 3デモ - "CommunityToolkit.Mvvm"NuGetパッケージ編
andrewkeepcoding
0
140
Featured
See All Featured
Refactoring Trust on Your Teams (GOTO; Chicago 2020)
rmw
24
2.2k
Fantastic passwords and where to find them - at NoRuKo
philnash
35
2.4k
実際に使うSQLの書き方 徹底解説 / pgcon21j-tutorial
soudai
111
35k
Easily Structure & Communicate Ideas using Wireframe
afnizarnur
185
15k
個人開発の失敗を避けるイケてる考え方 / tips for indie hackers
panda_program
58
14k
Mobile First: as difficult as doing things right
swwweet
215
8.5k
How to train your dragon (web standard)
notwaldorf
71
5.1k
YesSQL, Process and Tooling at Scale
rocio
160
13k
Reflections from 52 weeks, 52 projects
jeffersonlam
343
19k
Put a Button on it: Removing Barriers to Going Fast.
kastner
58
3k
XXLCSS - How to scale CSS and keep your sanity
sugarenia
240
1.2M
Making the Leap to Tech Lead
cromwellryan
123
8.4k
Transcript
Contractsで Compilerを賢くしよう Kotlin愛好会 vol5
About me •Kenji Abe •Cookpad Inc. •Android Developer •Twitter: @STAR_ZERO
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
今回の環境 •IntelliJ IDEA 2018.2.5 •Kotlin 1.3.0-rc-190
簡単な例
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) } }
Contractsあり @ExperimentalContracts fun isNonNull(s: String?): Boolean { contract { returns(true)
implies (s != null) } return s != null }
Contractsあり @ExperimentalContracts fun hoge(s: String?) { if (isNonNull(s)) { //
Smart Castしてくれる println(s.length) } }
Contractsなし fun runFunc(func: () -> Unit) { func() } fun
hoge() { var x: Int runFunc { x = 10 } // Variable 'x' must be initialized println(x) }
Contractsあり @ExperimentalContracts fun runFunc(func: () -> Unit) { contract {
callsInPlace(func, InvocationKind.EXACTLY_ONCE) } func() }
Contractsあり @ExperimentalContracts fun hoge() { var x: Int runFunc {
x = 10 } // エラーなし println(x) }
returns - implies
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
returns - implies •returns() •returns(value: Any?) ‣ true, false, null
•returnsNotNull()
returns - implies •implies ‣ == null, != null ‣
is, !is
Example 1 @ExperimentalContracts fun validate(s: String?) { contract { returns()
implies (s != null) } if (s.isNullOrEmpty()) { throw IllegalArgumentException() } }
Example 1 @ExperimentalContracts fun hoge(value: String?) { validate(value) println("length =
${value.length}") }
Example 2 @ExperimentalContracts fun isString(v: Any?): Boolean { contract {
returns(true) implies (v is String) } return v is String }
Example 2 @ExperimentalContracts fun hoge(v: Any?) { if (isString(v)) {
println("length = ${v.length}") } }
Example 3 @ExperimentalContracts fun castInt(v: Any?): Int? { contract {
returnsNotNull() implies (v is Int) } return v as? Int }
Example 3 @ExperimentalContracts fun hoge(v: Any?) { if (castInt(v) !=
null) { println("${v + v}") } }
Example 4 @ExperimentalContracts fun Any?.isString(): Boolean { contract { returns(true)
implies (this@isString is String) } return this is String }
Example 4 @ExperimentalContracts fun hoge(v: Any?) { if (v.isString()) {
println("length = ${v.length}") } }
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 }
Example 5 @ExperimentalContracts fun hoge(v: Any?) { if (stringOrInt(v)) {
println("length = ${v.length}") } else { println("plus = ${1 + v}") } }
callsInPlace
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
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
Example 1 @ExperimentalContracts fun runAtLeastOnce(func: () -> Unit) { contract
{ callsInPlace(func, InvocationKind.AT_LEAST_ONCE) } func() }
Example 1 @ExperimentalContracts fun hoge() { var x: Int runAtLeastOnce
{ x = 10 } println(x) }
Example 2 @ExperimentalContracts fun runAtMostOnce(func: () -> Unit) { contract
{ callsInPlace(func, InvocationKind.AT_MOST_ONCE) } func() }
Example 2 @ExperimentalContracts fun hoge() { var x: Int runAtMostOnce
{ x = 10 } // Variable 'x' must be initialized println(x) }
Example 3 @ExperimentalContracts fun runFuncs(func1: () -> Unit, func2: ()
-> Unit) { contract { // func1だけ設定 callsInPlace(func1, InvocationKind.EXACTLY_ONCE) } func1() func2() }
Example 3 @ExperimentalContracts fun hoge() { var x: Int runFuncs({
x = 10 }) { x = 20 } // Variable 'x' must be initialized println(x) }
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() }
Example 4 @ExperimentalContracts fun hoge() { var x: Int runFuncs({
x = 10 }) { x = 20 } println(x) }
Example 5 @ExperimentalContracts fun runFunc(func: () -> Unit) { contract
{ callsInPlace(func, InvocationKind.EXACTLY_ONCE) } func() }
Example 5 @ExperimentalContracts fun hoge() { var x: Int runFunc({
x = 10 }) // <- 括弧で括る // Variable 'x' must be initialized println(x) }
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 }
Example 6 @ExperimentalContracts fun hoge(v: Any) { var x: Int
if (complex(v) { x = 10 }) { println("length = ${v.length}") } println("x = $x") }
注意
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
まとめ
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?
ありがとうございました