Kotlin examples

example-1.kt

// Data classes

data class Something(val something: String)

val output = Something("test").toString() // Something(something=test)

val equal = Something("test2") == Something("test2") // true
val notEqual = Something("test3") == Something("test4") // false

example-2.kt

// Null safety and null coalescing

class UserInfo {
  val id: Int
  val name: String?
}

val name = userInfo.name ?: "a default name"

example-3.kt

// Type inference, operator overloading, mutability of primitives

val emptyThing = emptySet<String>()
val typeInferredThing = setOf("hello", "world")

val mutableThing = mutableSetOf("hello")
mutableThing += "world"

example-4.kt

// Expressions

val failableInt: Int? = try {
  Integer.parseInt(5)
} catch (e: NumberFormatException) {
  null
}

example-5.kt

// Functional

val evens = listOf(1, 2, 3, 4, 5).filter { it % 2 == 0 }

example-6.kt

// Parameter defaults, named parameters

data class Pizza(val toppings: Set<String> = setOf("cheese", "tomato"))

val defaultPizza = Pizza()
val withOnion = Pizza(toppings = setOf("cheese", "tomato", "onion"))

example-7.kt

// Enums, when expressions

enum class ContrivedExample {
  FIRST,
  SECOND,
  THIRD
}

fun convertEnumToString(thing: ContrivedExample): String {
  return when (thing) {
    ContrivedExample.FIRST -> "first"
    ContrivedExample.SECOND -> "second"
    else -> "unknown"
  }
}

example-8.kt

// Smart casting, string interpolation

val thing = "Test"

if (thing is String) {
  println("thing is a String with length ${thing.length}")
} else {
  println("thing isn't a String")
}

example-9.kt

// Ranges

for (i in 0..10) { } // 0 1 ... 10
for (i in 0 until 10) { } // 0 1 ... 9