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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.

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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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