API pollution, restrict the visibility. As necessary, use local extension functions, member extension functions, or top-level extension functions with private visibility.
retrieveOrder() ?. let { processCustomer(it.customer) } No extra variable retrieveOrder() ?. let { processCustomer(it.customer) } retrieveOrder() ?. customer ?. let { :: processCustomer } or ?.let
} fun makeDir(path: String) : File { val file = File(path) file.mkdirs() return file } Don’t overuse the scope functions! This is simpler! fun makeDir(path: String) = File(path).also { it.mkdirs() } OK, this one is actually fi ne :)
= 1, val depth: Int = 1, color: Color = Color.BLACK, description: String = "This is a 3d figure", ) Figure(color = Color.RED, description = "Red figure")
Weather() fun adjustSpeed(weather: Weather) = when (weather) { is Rainy -> Safe() is Sunny -> TODO() } Use expressions! Use when as expression body Use sealed classes with when
= order !! .customer !! .address !! .city “You may notice that the double exclamation mark looks a bit rude: it’s almost like you’re yelling at the compiler. This is intentional.” - Kotlin in Action
String) private var state: State? = null @BeforeEach fun setup() { state = State("abc") } @Test fun foo() { assertEquals("abc", state !! .data) } } class MyTest { class State(val data: String) private lateinit var state: State @BeforeEach fun setup() { state = State("abc") } @Test fun foo() { assertEquals("abc", state.data) } } - use lateinit
String?, val age: Int?) fun processPerson(person: Person) { val name = person.name if (name = = null) throw IllegalArgumentException("Named required") val age = person.age if (age == null) return println("$name: $age") }
String?, val age: Int?) fun processPerson(person: Person) { val name = person.name if (name = = null) throw IllegalArgumentException("Named required") val age = person.age if (age == null) return println("$name: $age") }
String?, val age: Int?) fun processPerson(person: Person) { val name = person.name if (name = = null) throw IllegalArgumentException("Named required") val age = person.age if (age == null) return println("$name: $age") }
String?, val age: Int?) fun processPerson(person: Person) { val name = person.name ? : throw IllegalArgumentException("Named required") val age = person.age ?: return println("$name: $age") }
Any?) : Boolean { val command = other as Command return command.id == id } override fun equals(other: Any?) : Boolean { return (other as? Command) ?. id == id }
0 .. args.size - 1) { println("$i: ${args[i]}") } } for (i in 0 until args.size) { println("$i: ${args[i]}") } for (i in args.indices) { println("$i: ${args[i]}") }
0 .. args.size - 1) { println("$i: ${args[i]}") } } for (i in 0 until args.size) { println("$i: ${args[i]}") } for (i in args.indices) { println("$i: ${args[i]}") } for ((i, arg) in args.withIndex()) { println("$i: $arg") }
= 1 to "one" // same but shorter fun namedNum2() = 1 to "one" fun main(args: Array<String>) { val pair = namedNum() val number = pair.first val name = pair.second }
= 1 to "one" // same but shorter fun namedNum2() = 1 to "one" fun main(args: Array<String>) { val pair = namedNum() val number = pair.first val name = pair.second } data class GameResult( val rank: Int, val name: String ) fun namedNum() = GameResult(1, "Player 1") fun main(args: Array<String>) { val (rank, name) = namedNum() println("$name, rank $rank") }
xyc """.trimIndent() val groups: List<String> = input.split("\n\n") var total = 0 for (group in groups) { val listOfSets: List<Set<Char >> = group.split("\n").map(String :: toSet) var result = listOfSets.first() for (set in listOfSets) { result = result intersect set } total += result.count() }
xyc """.trimIndent() val groups: List<String> = input.split("\n\n") var total = 0 for (group in groups) { val listOfSets: List<Set<Char >> = group.split("\n").map(String :: toSet) var result = listOfSets.first() for (set in listOfSets) { result = result intersect set } total += result.count() }
xyc """.trimIndent() val groups: List<String> = input.split("\n\n") var total = 0 for (group in groups) { val listOfSets: List<Set<Char >> = group.split("\n").map(String :: toSet) var result = listOfSets.first() for (set in listOfSets) { result = result intersect set } total += result.count() }
xyc """.trimIndent() val groups: List<String> = input.split("\n\n") var total = 0 for (group in groups) { val listOfSets: List<Set<Char >> = group.split("\n").map(String :: toSet) var result = listOfSets.first() for (set in listOfSets) { result = result intersect set } total += result.count() }
xyc """.trimIndent() val groups: List<String> = input.split("\n\n") var total = 0 for (group in groups) { val listOfSets: List<Set<Char >> = group.split("\n").map(String :: toSet) var result = listOfSets.first() for (set in listOfSets) { result = result intersect set } total += result.count() } Transforming data
xyc """.trimIndent() val groups: List<String> = input.split("\n\n") var total = 0 for (group in groups) { val listOfSets: List<Set<Char >> = group.split("\n").map(String :: toSet) var result = listOfSets.first() for (set in listOfSets) { result = result intersect set } total += result.count() } Transforming data Calculating the result
= groups.map { it.split("\n").map(String :: toSet) } val step2 = step1.sumOf { it.reduce { a, b - > a intersect b }.count() } Transforming data Calculating the result
= groups.map { it.split("\n").map(String :: toSet) } val step2 = step1.sumOf { it.reduce { a, b - > a intersect b }.count() } Transforming data Calculating the result
= groups.map { it.split("\n").map(String :: toSet) } val step2 = step1.sumOf { it.reduce { a, b - > a intersect b }.count() } Transforming data Calculating the result
= groups.map { it.split("\n").map(String :: toSet) } val step2 = step1.sumOf { it.reduce { a, b - > a intersect b }.count() } Transforming data Calculating the result
= groups.map { it.split("\n").map(String :: toSet) } val step2 = step1.sumOf { it.reduce { a, b - > a intersect b }.count() } Transforming data Calculating the result
= groups.map { it.split("\n").map(String :: toSet) } val step2 = step1.sumOf { it.reduce { a, b - > a intersect b }.count() } Transforming data Calculating the result groups.map { group -> group.split(nl).map(String :: toSet) }.sumOf { answerSets -> answerSets.reduce { a, b -> a intersect b }.count() }
remoteIP: String, val timestamp: Long ) fun analyzeLog(log: List<Request>) { val map = mutableMapOf<String, MutableList<Request >> () for (request in log) { map.getOrPut(request.url) { mutableListOf() } .add(request) } }
remoteIP: String, val timestamp: Long ) fun analyzeLog(log: List<Request>) { val map = mutableMapOf<String, MutableList<Request >> () for (request in log) { map.getOrPut(request.url) { mutableListOf() } .add(request) } } fun analyzeLog(log: List<Request>) { val map = log.groupBy(Request :: url) }
{ val actualValue = when { value < 0 - > 0 value > 100 -> 100 else - > value } } fun updateProgress(value: Int) { val actualValue = value.coerceIn(0, 100) }
builder.setFirstName("Anton"); builder.setLastName("Arhipov"); final TwitterBuilder twitterBuilder = new TwitterBuilder(); twitterBuilder.setHandle("@antonarhipov"); builder.setTwitter(twitterBuilder.build()); final CompanyBuilder companyBuilder = new CompanyBuilder(); companyBuilder.setName("JetBrains"); companyBuilder.setCity("Tallinn"); builder.setCompany(companyBuilder.build()); final Client client = builder.build(); System.out.println("Created client is: " + client);
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