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Guide

Coming from Kotlin and Swift

What maps directly from Kotlin or Swift, the five habits that will trip you up, and the property and coroutine features TorbScript leaves out.

when and switch look like match, an extension looks like extend, and String? means what you expect. The surface is close enough that a habit from either language often compiles and means something else.

At a glance#

Kotlin / SwiftTorbScriptNote
val / let, varconst, varconst also freezes everything inside the value
String? / Optional<String>String? (Option<String>)the same idea
data class Point(val x: Int) / struct Pointtype Point { x: Int }one keyword
sealed class Shape / enum Shapetype Shape { case Circle(radius: Float) }cases and fields in one declaration
interface / protocoltraita type says with Shape
fun Circle.area() / extension Circleextend Circle with Area { }an extension adds a trait
when (shape) { is Circle -> } / switchmatch shape { .Circle(radius) => ... }every case handled, no else needed
mutating func grow()var fn grow()the method says that it changes the value
a ?: b / a ?? ba ?? bthe same
!! / !nothingthere is no force unwrap
object Registrya shared type you create onceno hidden singleton
suspend fun / async funca function returning Task<Value>waiting is in the type
ktlint / SwiftFormattorb formatone layout, and --check fails a build
Hashable, Equatable, ComparableHash, Equals, Comparea trait is named after its method
@DslMarker, scope functionsnothingone rule for every configuration block

What changes in your code#

type Rectangle {
  var width: Float
  var height: Float

  fn area(): Float {
    width * height
  }
}

var box = Rectangle 3.0, 4.0
box.width = 5.0
print box.area()
// prints 20.0

There are no computed properties: area() is a method, and you call it. A field and a method never share a name, so you always know which one you are looking at.

What TorbScript does not have#

No property observers (willSet, didSet) and no get/set blocks. No lateinit and no two-phase initialization. No smart casts: take a value apart with match instead. No suspend keyword. Visibility is public or private to the file, nothing in between.

Habits to unlearn#

  • !! or ! to unwrap. Handle the None case, or give a fallback with ??.
  • apply, run, let or guard let. A configuration block has one form, and ? does what guard does.
  • An else arm only to satisfy the compiler. A match over all cases needs none, and an arm that can never match is an error.
  • while (true). Write loop { ... }; while true is an error that names it.
  • Overloading by parameter type. A name means one function; a default value covers most overloads.
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