Kotlin Quick Reference

fun main() {
    println("Hello")
}

val name = "Ada"

var count = 0

"$name is ${age + 1}"

"42".toInt()

"x".toIntOrNull()

42.toString()

var nickname: String? = null

nickname?.length

val name = nickname ?: "guest"

if (nickname != null) {
    println(nickname.length)
}

user?.let { println(it.name) }

val nums = listOf(3, 1, 2)

val mutable = mutableListOf<Int>()

nums.map { it * 2 }

nums.filter { it > 1 }

nums.sum()

nums.sorted()

users.sortedBy { it.age }

nums.reversed()

users.find { it.id == 7 }

users.groupBy { it.role }

val ages = mapOf("Ada" to 36)

ages.getOrDefault("Bob", 0)

for (n in nums) { }

for ((i, n) in nums.withIndex()) { }

for (i in 0 until 5) { }

val label = if (n % 2 == 0) "even" else "odd"

val desc = when (n) {
    0 -> "zero"
    in 1..9 -> "small"
    else -> "big"
}

fun add(a: Int, b: Int): Int = a + b

fun greet(name: String = "world") { }

val square = { n: Int -> n * n }

fun String.shout() = uppercase() + "!"

data class User(val name: String, val age: Int)

class Dog(val name: String) {
    fun bark() = "Woof"
}

open class Animal
class Dog : Animal()

sealed interface Result
data class Ok(val value: Int) : Result
data class Err(val message: String) : Result

object Config { val port = 8080 }

suspend fun load(): String { delay(500); return "done" }

runBlocking { println(load()) }

val n = try { text.toInt() } catch (e: NumberFormatException) { 0 }