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I'm wondering what the use is of the asterisk (*) symbol in this syntax? I'm obviously new to Scala. I googled but am probably googling the wrong thing. Any help is appreciated.

Cheers!

Its called as "var args" (variable arguments).

def concat(strs: String*): String = strs.foldLeft("")(_ ++ _)
Scala REPL
scala> def concat(strs: String*): String = strs.foldLeft("")(_ ++ _)
concat: (strs: String*)String
scala> concat()
res6: String = ""
scala> concat("foo")
res7: String = foo
scala> concat("foo", " ", "bar")
res8: String = foo bar
                Thanks, that does it. I'm very much aware of the concept, but unfortunately I read just one tutorial for scala and it's been some months ago. If I revisited it, it would have been enough. Unfortunately, I went by stupid assumption it's a type :$
– hummingBird
                Aug 9, 2018 at 10:21
                @hummingBird You can easily see whether it's a type constructor by trying it out in isolation: type A = (Int*) doesn't compile. By the way: type A = (=> Int) also doesn't compile. So, those things are not type constructors, they are rather modifiers that determine how methods receive their arguments. And, if it solves your problem, could you please accept the answer then?
– Andrey Tyukin
                Aug 9, 2018 at 10:42
                @AndreyTyukin thanks for the explanation. I actually clicked several times, but one cannot accept an answer in <10min. Then I went for a break and now that I'm here - BOOM :).
– hummingBird
                Aug 9, 2018 at 11:13
This is called a repeated parameter (see Section 4.6.3 of the Scala Language Specification).
Repeated Parameters allow a method to take an unspecified number of arguments of the same type T, which are accessible inside the method body bound to a parameter of type Seq[T].
In your case, inside the method m, the parameter a will be bound to a Seq[String].
That's the syntax to define a method that take a variable number of arguments.
Your m method can take 0, 1 or more arguments and these are all valid invocations:
m("hello")
m("hello", "world")
You can also pass a collection to that method if you use the appropriate type hint:
val words = Seq("hello", "world")
m(words: _*)
You can play around with this code here on Scastie (where I implemented m as the concatenation of the input strings).
        
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