assigning multiple vals in conditionals

Question

In Java I often find myself assigning to multiple final variables in each branch of a conditional like so:

final _ x;
final _ y;
if (_) {
  x = _;
  y = _;
} else {
  x = _;
  y = _;
}

In Scala I am aware that a single val can be assigned using the technique:

val x = {
  if (_) {
    _;
  } else {
    _;
  }
}

In fact, the above method can be modified to assign to multiple variables by having the block return a tuple that is pattern matched to variables like:

{
  if (_) {
    _;
  } else {
    _;
  }
} match { case (x, y) => _ }

But I find this syntax to be quite awkward. Is there a simpler way, ideally similar to the Java code, to do what I want?

Answer 1

scala> val (x,y) = if (true) (3,"blah") else (1,"blis")
x: Int = 3
y: String = blah

It looks like a tuple assignment but it's actually assigning to multiple vals. (OK, it's actually both.)

Answer 2

Yes, you can specify multiple instances that you want your values to be assigned to, much like the cases in a match statement (and using the same underlying concept - unapply). THe most typical way you see this is done is in the form of a deconstructed tuple, such as (incorporating the if-else as per your question):

val (x,y,z) = if (true) (x_value, y_value, z_value) else (alt_x, alt_y, alt_z)

(much as shown in @jwvh's answer)

This can be taken further, to utilise the unapply method for any data type that has it (including all case classes). Eg:

scala> val head :: tail = if (true) List(3,4,5,6) else List(9,8,7)
head: Int = 3
tail: List[Int] = List(4, 5, 6)

or

scala> case class Foo(ix: Int, bar: String)
defined class Foo

scala> val f@Foo(the_ix, the_bar) = if (true) Foo(2, "baz") else Foo(5, "wibble")
f: Foo = Foo(2,baz)
the_ix: Int = 2
the_bar: String = baz

scala> f
res3: Foo = Foo(2,baz)

scala> the_ix
res4: Int = 2