MultiMap

MultimapBuilder.treeKeys().arrayListValues().build<Int, Move>()

List.fastForEach

/**
 * Iterates through a [List] using the index and calls [action] for each item.
 * This does not allocate an iterator like [Iterable.forEach].
 */
@OptIn(ExperimentalContracts::class)
internal inline fun <T> List<T>.fastForEach(action: (T) -> Unit) {
    contract { callsInPlace(action) }
    for (index in indices) {
        val item = get(index)
        action(item)
    }
}

kotlin.math.max()

kotlin.comparisons.maxOf()

flatten()

transform

flatten().map { it.idOfEntity }

flatten { it.idOfEntity }

flatten

addAll()

map

public inline fun <T, R> Iterable<Iterable<T>>.flatten(transform: (T) -> R): List<R> {
    val result = ArrayList<R>()
    for (elementIterable in this) {
        for (element in elementIterable) {
            result.add(transform(element))
        }
    }
    return result
}

Map<String, T> + Map<String, T>

Map<String, T>.distinct()

plus

distinct

fun <R> task(body: () -> R): R = TODO()
fun <P1, R> task(body: (P1) -> R): R = TODO()

fun main() {
  // overload ambiguity
  task {
    33
  }
}

fun <P1, R> task(body: (P1) -> R): R = TODO()
fun <P1, P2, R> task(body: (P1, P2) -> R): R = TODO()

fun main() {
  task { v: Int -> 33 }
}

java.lang.IllegalStateException: Symbol for kotlin.collections/mutableMapOf|-4813910536206556932[0] is unbound
	at org.jetbrains.kotlin.ir.symbols.impl.IrBindablePublicSymbolBase.getOwner(IrPublicSymbolBase.kt:52)

Result

onSuccess

onFailure

ConcurrentHashMap<Int, String>().getOrPut(1) { null } // compiles just fine, but it'll throw in runtime
mutableMapOf<Int, String>().getOrPut(1) { null } // compiler error: Null can not be a value of a non-null type String

to

val squared = mapOf { // this refers to some MapBuilderScope<K,V> with builder inference
    1 to 1 // `to` is only visible in the `MapBuilderScope`
    2 to 4
    3 to 9
}

fun getMap(): Map<String, String> {
    return buildMap {
      if (A) {
        put(key, "A")
      } else {
        put(key, "B")
      }
    }
  }

Type mismatch.
Required:
Unit
Found:
String
Type mismatch.
Required:
Unit
Found:
TypeVariable(V)?
Type mismatch.
Required:
Unit
Found:
String?

return buildMap {
      put(key, if (A) "A" else "B")
    }

typealias Null = Nothing?

class Info<T>(val description: String, val payload: T, ...)

interface Base<T> {
    fun getInfo(): List<Info<T>>
}

class Derived: Base<Null> {
    override fun getInfo() = listOf(Info("...", null, ...), ...)
}

class Derived: Base<Nothing?>

Unit

kotlin.time.Duration

java.time.temporal.TemporalAmont

Instant.now() + 5.seconds

TemporalAmont

we can <u>underline</u>,<b>bold</b> or <i>hyphenate</i>

commonMain

fun String.remove(pattern: String) = replace(Regex(pattern), "")
fun String.remove(regex: Regex) = replace(regex, "")

fun String.get(regex: Regex) = replace(regex, "$1")

Number.minOrNull()

.max()

.min()

fun <K, V> Iterable<Map<K, V>>.merge(): Map<K, V>

-jdk7

-jdk8

indy

kotlin.Result

value

kotlin.Result

We are working in other directions of making signalling error handling more pleasant to use in Kotlin.

// all T - java classes implementing ViewDataBinding, each providing a static `bind` method
// ViewDataBinding - a Java abstract class (with no declaration of `bind`)

interface BindingAware<T : ViewDataBinding> {
    var f: T

    fun bind(v: View) {
        // f = T.bind(a)  // <= how to call static method provided by class behind T?
    }
}

expect

actual

expect

actual

fun <T> Iterable<T>.withIndex(): Iterable<IndexedValue<T>>

fun <T> Iterable<IndexedValue<T>>.withoutIndex(): List<T> = map(IndexedValue<T>::value)