Kotlin Scala Differences Cheat Sheet

Feature	Kotlin	Scala
Function Keyword	fun	def
Nullability	Default not nullable except by adding ? at the end of variable type	Null is discouraged, but no hard check
Null Check	Use ?. and/or ?:	Use Option
Lambda/Anonymous Functions	Need to be surrounded with {}	Can be used anywhere
Covariant	[out T]	[+T]
Contravariant	[in T]	[-T]
Pattern Matching	(partial) when statement	(full) match/case
Default Case	else ->	case _ =>
Loop a Range	i in 1..10 step 2 (closed) i in 1 until 10 step 2 (half-closed)	i <- 1 to 10 by 2 (closed) i in 1 until 10 by 2 (half-closed)
Read File into Strings	File(fileName).useLines { it.toList() }	scala.io.Source.fromFile("file.txt").mkString
For Comprehension (for/yield)	No Equivalent	Supported
Companion Object	companion object keyword inside class	object keyword besides class
New Immutable Sequence	listOf("one", "two", "one")	Seq("one", "two", "one")
New Immutable Set	setOf("one", "two", "three")	Set("one", "two", "one")
New Immutable Map	mapOf("key1" to 1, "key2" to 2, "key3" to 3, "key4" to 1)	Map("key1" -> 1, "key2" -> 2, "key3" -> 3, "key4" to 1)
Top Level Functions (Package Level)	Supported	Will be supported in Scala 3
Extension Functions	fun Any?.toString(): String { if (this == null) {return "null"} return toString()}	extension (c: Circle) def circumference: Double = c.radius * math.Pi * 2
Operator Overloading	with operator infix keyword	operators are just normal functions
Regex String	"[0-9]".toRegex()	"[0-9]".r
Tuple 2	Pair(a, b)	(a, b)
Tuple 3	Triple(a, b, c)	(a, b, c)
Destructuring Assignment	Objects with componentN() (data classes and collections)	Objects with unapply() (extractors like case classes)
Tail Recursive Function	tailrec keyword	@tailrec annotation
Multiple Inheritance Resolution	Must override function in question manually	Later trait wins
Class Inheritance	only with open or abstract keyword	allowed
The sealed keyword	sealed class is something like enum	sealed types are confined in its source file
Secondary/Auxiliary Constructors	constructor keyword	this() functions
Reference Equality (the Java ==)	===	eq
Map Entry Literal	k to v	k -> v