Being new to Scala (2.9.1), I have a List[Event]
and would like to copy it into a Queue[Event]
, but the following Syntax yields a Queue[List[Event]]
instead:
val eventQueue = Queue(events)
For some reason, the following works:
val eventQueue = Queue(events : _*)
But I would like to understand what it does, and why it works? I already looked at the signature of the Queue.apply
function:
def apply[A](elems: A*)
And I understand why the first attempt doesn't work, but what's the meaning of the second one? What is :
, and _*
in this case, and why doesn't the apply
function just take an Iterable[A]
?
a: A
is type ascription; see What is the purpose of type ascriptions in Scala?
: _*
is a special instance of type ascription which tells the compiler to treat a single argument of a sequence type as a variable argument sequence, i.e. varargs.
It is completely valid to create a Queue
using Queue.apply
that has a single element which is a sequence or iterable, so this is exactly what happens when you give a single Iterable[A]
.