Enums and associated values

A score can be pending or recorded. Encoding those states as unrelated strings and numbers allows inconsistent combinations. An enum declares a defined set of cases, and associated values carry data belonging to a particular case.

Unlike a raw value, which gives a case a fixed underlying representation, an associated value is supplied for a particular instance. A switch can match the case and extract that instance’s value. Covering every enum case makes missing state handling a compile-time concern.

Save this complete program as main.swift and run it with the Swift toolchain. No separate input file is needed.

Swift · complete program

enum Result {
  case pending
  case recorded(Int)
}
let result = Result.recorded(80)
switch result {
case .pending: print("Awaiting result")
case .recorded(let score): print("Score:", score)
}

Expected output

Score: 80

Follow the execution

The recorded instance carries 80. Matching that case binds score inside the branch and prints it. There is no separate “pending” flag that could accidentally coexist with a recorded score.

Try this program in the Swift compiler. Paste the complete source above.

Your task: What would Result.pending carry?

Swift · complete program

enum Result {
  case pending
  case recorded(Int)
}
let result = Result.recorded(80)
switch result {
case .pending: print("Awaiting result")
case .recorded(let score): print("Score:", score)
}

Worked answer

It carries no score because that case declares no associated value. The matching branch can show an absence message without inventing a number.

Use enums for meaningful alternatives, not just to hide strings. Adding a case may require updating exhaustive switches. Raw-value initialization can fail for an unknown value and therefore often returns an optional.

It carries no score because that case declares no associated value. The matching branch can show an absence message without inventing a number. Use enums for meaningful alternatives, not just to hide strings.

Further reading: official Swift language guide.