Case classes in Scala

A Lighthouse record with generated printing and equality, taken apart by a match.

// a case class is an immutable record whose fields are public vals
case class Lighthouse(name: String, heightM: Int, flashSec: Int)

// no new keyword is needed to build one
val portland: Lighthouse = Lighthouse("Portland", 41, 5)

// toString is generated, printing the class name and the fields
val printed: String = portland.toString

// equality compares the fields, so two separate builds are equal
val twin: Lighthouse = Lighthouse("Portland", 41, 5)
val sameLight: Boolean = portland == twin

// match takes the value apart by position, binding each field to
// a name; a literal in one slot only matches that exact value
def describe(light: Lighthouse): String = light match
  case Lighthouse(name, height, 5) => s"$name, ${height}m, quick"
  case Lighthouse(name, _, secs) => s"$name every ${secs}s"

val summary: String = describe(portland)

How it works

1. case class Lighthouse(name: String, heightM: Int, flashSec: Int) declares the record, and Lighthouse("Portland", 41, 5) builds one with no new keyword.
2. portland.toString is generated from the fields, and portland == twin compares field by field, so two separately built lighthouses come out equal.
3. case Lighthouse(name, height, 5) binds fields by position and matches only when the third is that literal, leaving case Lighthouse(name, _, secs) for the rest.

Keywords and builtins used here

• Boolean
• Int
• Lighthouse
• String
• case
• class
• def
• describe
• match
• val

The run, in numbers

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Tokens

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Three-star pace

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Step 1 of 3 in Case classes & enums, step 16 of 27 in Language basics.

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