Boolean?.orFalse()

Files.createDirectories

PosixFileAttribute

goto

fun <T> List<T>.slice(fromIndex: Int, toIndex: Int): List<T>

fun <T> List<T>.slice(indices: IntRange): List<T>

internal fun Iterable<*>.containerName(): String {
   return when (this) {
      is List -> "List"
      is Set -> "Set"
      is Map<*, *> -> "Map"
      is ClosedRange<*>, is OpenEndRange<*> -> "Range"
      is Collection -> "Collection"
      else -> "Iterable"
   }
}

Map

Ranges

fun <T, K> List<T>.chunkBy(selector: (T) -> K): List<List<T>> {
    val result = mutableListOf<MutableList<T>>()
    var lastKey: K? = null
    for (item in this) {
        if (selector(item) != lastKey) result.add(mutableListOf(item)).also { lastKey = selector(item) }
        else result.last().add(item)
    }
    return result
}

 data class Person(val age: Int)

val persons = listOf(Person(23), Person(12), Person(23), Person(23), Person(22))
val chunkBy = persons.chunkBy { it.age }

@Test
    fun test1() {
        val map = LinkedHashMap<String, Int>()
        val n = 3
        repeat(n) {
            map["$it"] = it
        }

        println(map)
        val iterator = map.iterator()
        var count = 0
        while (iterator.hasNext()) {
            val entry = iterator.next()
            iterator.remove()
            println("${entry.key}=${entry.value}")
//            assertEquals(count++, entry.value)
        }
    }

{0=0, 1=1, 2=2}
0=0
1=1
2=2

{0=0, 1=1, 2=2}
null=0
null=1
null=2

{0=0, 1=1, 2=2}
null=null
null=null
null=null

ConcurrentModificationException: The backing map has been modified after this entry was obtained.

for ((index, value) in list.withIndex())  // Correct: the class name is IndexedValue: index first, value second.

val (time, value) = measureTimedValue { } // Wrong! the class name is TimedValue, yet it's actually value first, time second.

Double.toString(decimals: Int)

Duration

java.lang.Character.isLetter(int codePoint)

j.l.Character

Duration

Double

Double

d

d

Long

Int

Uuid

Number.toBigDecimal()

Int.toBigDecimal()

Double.toBigDecimal()

BigDecimal

fun Number.toBigDecimal(): BigDecimal = when(this) {
    is Short -> this.toBigDecimal()
    is Int -> this.toBigDecimal()
    .......
}

Result

Throwable | (R - Throwable) | SuccessfulThrowable<R>

KInterface

kotlin.reflect

KClass

isFun

@ExperimentalEncodingApi

interface Foo {
    val selfValue: String

    fun doSomething(): String {
        if (this::class == Foo::class) {
            return "Foo"
        } else {
            return "${super.doSomething()}.$selfValue"
        }
    }
}

val str = StringBuilder("The value of your purchase is ").apply {
    ...do things...
    append(things)
}.toString()

buildString

String

CharSequence

val str = buildString("The value of your purchase is ".length + 16) {
    append("The value of your purchase is ")
    ...do things...
    append(things)
}

TreeMap

kotlin

Kotlinx

listOf(1, 2, 3).sum()
listOf(1.toBigDecimal(), 2.toBigDecimal()).sum()  // Error
listOf(1.toBigDecimal(), 2.toBigDecimal()).sumOf { it }  // OK

sumOf

BigDecimal

sum

bisect_left

bisect_right

IntRange.size

fun <T> Sequence<T>.catch(action: suspend SequenceScope<T>.(Throwable) -> Unit): Sequence<T> {
    return sequence {
       try {
          forEach { yield(it) }
       } catch (t: Throwable) {
          action(t)
       }
    }
}

and

or

kotlin.experimental

AtomicLong

Lock

Map

kotlinx.coroutines.sync.Mutex

veryLargeList.Order().Take(10).ToList();

veryLargeList.asSequence().sorted().take(10).toList()