Why am i unable to use this simple code in my kotlin repl

Question

I receive this error -----

error: incompatible types: IntRange and Int
3..12 -> print("Good fish name")

var fishName = "anyname"
when (fishName.length){
0 -> print("Error")
3..12 -> print("Good fish name")
else -> {
print("OK fish name")
} 
}

---

I was expecting to be able to have the message "Good fish name" be printed out.

Answer 1

A when construct is comparing the argument fishName.length which is an Int with each of the values in the when construct. The first 0 is an Int, but 3..12 is an IntRange; each must be an Int for the equality test.

Here are three solutions:

Pass in a load of Ints...

    when (fishName.length){
        0 -> print("Error")
        3,4,5,6,7,8,9,10,11,12 -> print("Good fish name")
        else -> {
            print("OK fish name")
        }
    }

or use this alternate form, changing the zero test also to be a range:

    when (fishName.length){
        in 0..0 -> print("Error")
        in 3..12 -> print("Good fish name")
        else -> {
            print("OK fish name")
        }
    }

UPDATE From @gidds - "Kotlin lets you mix individual values ... with predicates":

    when (fishName.length){
        0 -> print("Error")
        in 3..12 -> print("Good fish name")
        else -> {
            print("OK fish name")
        }
    }

See https://kotlinlang.org/docs/control-flow.html#when-expression