Question

Often times I have a desire to create variables scoped to an if statement. Some computations only relate to a particular ‘if’ statement – to pollute the outer scope with temporary variables smells bad.

What I would like to do:

val data = (whatever)

if (val x = data*2+5.4345/2.45; val y = data/128.4; x*y < 10) 
  x * y
else
  x * 2

println(x) //ERROR!

One alternative is rather messy:

val data = (whatever)

if (data*2+5.4345/2.45*data/128.4 < 10) 
  data*2+5.4345/2.45*data/128.4
else
  data*2+5.4345/2.45 * 2

The obvious alternative I’m trying to avoid:

val data = (whatever)
val x = data*2+5.4345/2.45
val y = data/128.4

if (x*y < 10) 
  x*y
else
  x * 2

println(x) //OK

Is something like this possible in Scala? Is there a decent workaround? If not, what other languages support an idea like this?

Answer 1

Since if in Scala is an expression, i.e. it returns a value, normally you’d be setting some value to the result of your if expression. So your third alternative is just fine: put it in a code block, i.e.

val data = (whatever)
val myValue = {
  val x = data*2+5.4345/2.45
  val y = data/128.4

  if (x*y < 10) 
    x*y
  else
    x * 2
}

None of the vals declared within the block are available outside it.