scala differences between 2 functions syntaxes

Question

I'm trying to understand the differences between these 2 syntaxes in scala and why they have not the same result.

testVal

and

testVal2

are not defined in the same way

object FunctionVsVal2 extends App {


  val testVal: () => Int = {
    val r = util.Random.nextInt
    () => r
  }

  val testVal2: () => Int = () => {
    val r = util.Random.nextInt
    r
  }

  println(testVal())
  println(testVal())

  println(testVal2())
  println(testVal2())
}

Thanks

Alexey Romanov · Accepted Answer · 2022-05-29 16:01:58Z

4

testVal2 is a lambda expression. Each time you call testVal2(), it evaluates

{
  val r = util.Random.nextInt
  r
}

and so returns a new value.

testVal is a block expression. It calculates r first and then returns () => r (the last expression in the block), so each time you call testVal(), the same r is used.

answered May 29, 2022 at 16:01

Alexey Romanov

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3 Comments

user1361815 Over a year ago

if testVal2 is called each time why : println(testVal2 eq testVal2) prints true ? I was expecting to be false

Alexey Romanov Over a year ago

testVal2 eq testVal2 checks that testVal2 is the same object as testVal2. Why do you expect it not to be? It's unrelated to what happens when you apply testVal2 by writing testVal2().

Alexey Romanov Over a year ago

In both cases the body of the lambda, the part after () =>, is called each time you call testVal1/2(). The difference is what these bodies are; in testVal1 it's just r, in testVal2 it's { val r = util.Random.nextInt; r }. Does this help more?

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