inline

FooKt.myInlinedFun()

interface Validator<T> {
  fun validate(input: T)
  fun and(other: Validator<T>): Validator<T> = TODO()
}

fun <T> andExternal(v1: Validator<T>, v2: Validator<T>): Validator<T> = TODO()

fun <T> isNotEmpty(): Validator<T> = TODO()
fun <T> isNotBlank(): Validator<T> = TODO()

fun doStuff(validator: Validator<String>) { }

fun main() {
  // isNotEmpty is highlighted: "not enough information to infer type variable T"
  doStuff(isNotEmpty().and(isNotBlank()))
  // no error when using external variant of "and", inferred as String!
  doStuff(andExternal(isNotEmpty(), isNotBlank()))
}

Class<SomeEnumType>

KType

typeOf<SomeEnumType>()

myMutableInt = myMutableInt + 2

myMutableInt += 2

myMutableInt = myMutableInt.coerceIn(10, 100)

myMutableInt .= coerceIn(10,100) //not valid syntax

inline fun <reified T> proxy() = (something...) as T

val proxy = proxy<MyClass>()

MqttMessage

fun createMessage(message: String): MqttMessage {
    val array = message.map { it.toByte() }
            .toByteArray()
    return MqttMessage(array)
}

fun createMessage(message: String): MqttMessage = message.map { it.toByte() }
        .toByteArray()
        .map { MqttMessage(it) }

Number

interface Number<N: Number<N> : Comparable<N> {
    operator fun plus(other: N): N
    operator fun minus(other: N): N
    operator fun times(other: N): N
    operator fun div(other: N): N
    operator fun unaryMinus(): N

    val minValue: N
    val maxValue: N

    fun inverse(): N

    fun toDouble(): Double
    fun toFloat(): Float
    fun toLong(): Long
    fun toInt(): Int
    fun toChar(): Char
    fun toShort(): Short
    fun toByte(): Byte
}

spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=create-drop

try-with-resources

// Java
DataSource ds = createDataSource();
try (Connection connection = ds.getConnection()) {
    // ...
    // just throw exception for simulation
    throw new IllegalStateException()
    // ...
} catch (SQLException e) {
    e.printStackTrace()
}

use

// Kotlin
val ds: DataSource = createDataSource()
try {
    dataSource.connection.use { connection ->
        // just throw exception for simulation
        throw IllegalStateException()
    }
} catch (e: SQLException) {
    e.printStackTrace()
}

SQLException

IllegalStateException

SQLException

java.sql.Connection.getConnection()

use

with

with

run

but even if you don't need

, you can just always use

with

with

with

is

val isValid = true => {"isValid": true}

is

?valid=true => val isValid = true

?ssValid=true

@JsonProperty("valid")

is

foo

isFoo()

-Werror

tailrec fun TreeNode.findMin(): TreeNode = left?.findMin() ?: this

tailrec fun TreeNode.findMin(): TreeNode = if (left == null) this else left!!.findMin()

tailrec

BigDecimal

kotlin

operator fun BigDecimal.plus(other: BigDecimal): BigDecimal = add(other, MathContext.DECIMAL128)

operator fun BigDecimal.minus(other: BigDecimal): BigDecimal = subtract(other, MathContext.DECIMAL128)

operator fun BigDecimal.div(other: BigDecimal): BigDecimal = divide(other, MathContext.DECIMAL128)

operator fun BigDecimal.times(other: BigDecimal): BigDecimal = multiply(other, MathContext.DECIMAL128)

div

@kotlin.internal.InlineOnly
public inline operator fun BigDecimal.div(other: BigDecimal): BigDecimal = this.divide(other, RoundingMode.HALF_EVEN)

DECIMAL128

1.toBigDecimal() / 3.toBigDecimal()

1

kotlin

val last3 = myList[^3..]
val first3 = myList[..3]

when (numA) {
   <  numB -> foo()
   == numB -> bar()
   >  numB -> baz()
}

val defaultInt = default(int)

default

where

typealiases

override fun load(id: String): Mono<StoredRequest?> {
        val storedRequest: StoredRequest? = memory[id]
        return Mono.just(null);
    }

for (x in foo::class.memberProperties)

File file = new File(
	getClass().getClassLoader().getResource("database.properties").getFile()
);