I am new to Scala and have some question about why string::List() works List()::s doesn't?I also want to know if ListBuffer works better than ::?
val columnNames :List[String] = ['foo','bar']
val work :List[String] = List()
for (s <- columnNames) {
s match {
//this doesn't compile
//case workPattern => work :: s
//this works
case workPattern => s :: work
// this also works
case workPattern => work :: List(s)
}
a :: b literally means "add an element a at the beginning of a list b".
It creates new list with a as a head and b as a tail.
To append element to list you can use ++
or something like this
work ::: "foo" :: Nil, the latter isn't very efficient, of course.
For the second part of a question, as stated in the documentation:
Time: List has O(1) prepend and head/tail access.
Most other operations are O(n) on the number of elements in the list.
This includes the index-based lookup of elements, length, append and reverse.
Space: List implements structural sharing of the tail list.
This means that many operations are either zero- or constant-memory cost.
So it depends on size and types of operations you need to perform which is preferable performance-wise.
The function you call at s :: work is List.::. Scala String is just an alias for Java's string, hence does not expose operators such as ::. s :: work is equivalent to work.::(s).
For more information you can refer How to add elements to a List in Scala (List, ListBuffer) and Scala List class examples: range, fill, tabulate, appending, foreach, more ... by the great Alvin Alexander.
