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If I create a Set in Scala using Set(1, 2, 3) I get an immutable.Set.
scala> val s = Set(1, 2, 3)
s: scala.collection.immutable.Set[Int] = Set(1, 2, 3)
Q1: What kind of Set is this actually? Is it some hash-set? What is the complexity of look-ups for instance?
Q2: Where can I read up on this "set-creating" method? I thought that it was the apply method but the docs says "This method allows sets to be interpreted as predicates. It returns true, iff this set contains element elem."
Similarly, if I create a List using List(1, 2, 3), I get
scala> val l = List(1, 2, 3)
l: List[Int] = List(1, 2, 3)
scala> l.getClass
res13: java.lang.Class[_] = class scala.$colon$colon
Q3: Again, what do I get? In this case I can't even immediately tell if it's mutable or not, since it's not even part of the scala.collection-package. Why does this live in the scala package?
Q4: Where in the API can I read about this "list-creating" method?
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A Set is unordered and can't have duplicate items. Sequences ( Array , List , Vector , etc) are ordered and can have repeated elements. Save this answer.
Scala Set is a collection of pairwise different elements of the same type. In other words, a Set is a collection that contains no duplicate elements. There are two kinds of Sets, the immutable and the mutable.
A list is a collection which contains immutable data. List represents linked list in Scala. The Scala List class holds a sequenced, linear list of items. Following are the point of difference between lists and array in Scala: Lists are immutable whereas arrays are mutable in Scala.
Syntax for defining a Scala List. val variable_name: List[type] = List(item1, item2, item3) or val variable_name = List(item1, item2, item3) A list in Scala is mostly like a Scala array. However, the Scala List is immutable and represents a linked list data structure.
Q1: In this specific case you get a Set3 which is an immutable set of exactly three arguments. Presumably it uses if-else if-else to check inclusion. If you create a set of more than 4 elements, you get an immutable hash set.
Q2: You need to look at the apply method of the object Set, not the class. The apply method of the Set class is what is called when you do someSet(something).
Q3: scala.:: is a non-empty immutable singly linked list (if you do List() without arguments, you get Nil which is an immutable empty list). It lives in the scala package because it is considered so basic that it belongs in the base package.
Q4: See Q2.
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Just to add to sepp2k's excellent answer to Q3, where he says
It lives in the
scalapackage because it is considered so basic that it belongs in the base package.
This applies to Scala 2.7
In Scala 2.8, the collections classes have been reorganized, and now the :: class lives in scala.collection.immutable, and the name scala.:: is a type alias for scala.collection.immutable.::.
Welcome to Scala version 2.8.0.RC5 (OpenJDK 64-Bit Server VM, Java 1.6.0_18).
Type in expressions to have them evaluated.
Type :help for more information.
scala> val l = List(1, 2, 3)
l: List[Int] = List(1, 2, 3)
scala> l.getClass
res0: java.lang.Class[_] = class scala.collection.immutable.$colon$colon
scala> scala.::
res1: collection.immutable.::.type = scala.collection.immutable.$colon$colon$@6ce5d622
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