Default & named arguments in Scala

Parameters that carry defaults, and calls that name their arguments instead of ordering them.

// A parameter with a default may be left out by the caller.
def ticketLine(film: String, seats: Int = 1, matinee: Boolean = false) =
  val each = if matinee then 8.5 else 12.0
  f"$film%-12s $seats seat(s) ${each * seats}%6.2f"

// A default is evaluated only when the argument is left out.
def refund(paid: Double, fee: Double = 1.5): Double = paid - fee

def boxOffice(): Unit =
  // Omitted parameters fall back to their defaults.
  println(ticketLine("Nosferatu"))
  // Named arguments may be written in any order.
  println(ticketLine(seats = 3, film = "Solaris"))
  // Positional first, then named to skip a middle parameter.
  println(ticketLine("Stalker", matinee = true))
  println(refund(24.0))
  println(refund(24.0, fee = 0.0))

How it works

1. def ticketLine(film: String, seats: Int = 1, matinee: Boolean = false) gives two of its three parameters defaults.
2. ticketLine("Nosferatu") leans on both defaults, while ticketLine(seats = 3, film = "Solaris") names its arguments and reverses their order.
3. ticketLine("Stalker", matinee = true) passes one argument by position and names the last to skip over seats.

Keywords and builtins used here

• Boolean
• Double
• Int
• String
• Unit
• boxOffice
• def
• else
• if
• refund
• then
• ticketLine
• val

The run, in numbers

Lines

17

Characters to type

720

Tokens

123

Three-star pace

75 tpm

At the three-star pace of 75 tokens a minute, this run takes about 98 seconds.

Type this snippet

Step 2 of 3 in Functions, step 8 of 27 in Language basics.

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