Question

Why doesn’t this work in scala:

val cloz: (Int,String => String) = (num: Int, str: String) => {
    str+"-"+num
}

I see a few examples of closures being defined with only 1 arg, like this:

val thingy: (Int => Int) = (num: Int) => {
    num * 2
}

But absolutely nowhere (including Scala ebooks) could I find any information explaining the syntax of “val” closures.

Thanks!
Jamie

Answer 1

The correct syntax is:

val cloz: (Int, String) => String = (num: Int, str: String) => {
    str + "-" + num
}

By the way, in this simple case you can also simplify expression like this (especially if you already explicitly specifying the type of the function):

val cloz: (Int, String) => String = (num, str) => str + "-" + num 

---

Update

You can also use REPL to explore Scala – it’s very nice tool. You can start it just by starting scala without any arguments. Here is example session:

scala> val cloz = (num: Int, str: String) => str + "-" + num
cloz: (Int, String) => java.lang.String = <function2>

scala> val cloz: (Int, String) => String = (num: Int, str: String) => {
     |     str + "-" + num
     | }
cloz: (Int, String) => String = <function2>

scala> val cloz: (Int, String) => String = (num, str) => str + "-" + num
cloz: (Int, String) => String = <function2>

scala> def printCloz(cloz: (Int, String) => String, num: Int, str: String) = print(cloz(num, str))
printCloz: (cloz: (Int, String) => String, num: Int, str: String)Unit

As you can see it not only allows you to interactively execute code, but also prints type information if you define something.