Question

Possible Duplicate:
Tuple parameter declaration and assignment oddity

In Scala, one can do multiple-variable assignment to tuples via:

val (a, b) = (1, 2)

But a similar syntax for assignment to variables doesn’t appear to work. For example I’d like to do this:

var (c, d) = (3, 4)
(c, d) = (5, 6)

I’d like to reuse c and d in multiple-variable assignment. Is this possible?

Answer 1

This isn’t simply “multiple variable assignment”, it’s fully-featured pattern matching!

So the following are all valid:

val (a, b) = (1, 2)
val Array(a, b) = Array(1, 2)
val h :: t = List(1, 2)
val List(a, Some(b)) = List(1, Option(2))

This is the way that pattern matching works, it’ll de-construct something into smaller parts, and bind those parts to new names. As specified, pattern matching won’t bind to pre-existing references, you’d have to do this yourself.

var x: Int = _
var y: Int = _

val (a, b) = (1, 2)
x = a
y = b

// or

(1,2) match {
  case (a,b) => x = a; y = b
  case _ =>
}