Scala's '::' operator, how does it work?

Question

In Scala, I can make a caseclass, case class Foo(x:Int), and then put it in a list like so:

List(Foo(42))

Now, nothing strange

Answer 1

From the Spec:

6.12.3 InfixOperations An infix operator can be an arbitrary identifier. Infix operators have precedence and associativity defined as follows.

...

The associativity of an operator is determined by the operator’s last character. Operators ending in a colon ‘:’ are right-associative. All other operators are left- associative.

You can always see how these rules are applied in Scala by printing the program after it has been through the 'typer' phase of the compiler:

scala -Xprint:typer -e "1 :: Nil"

val r: List[Int] = {
   val x$1: Int = 1;
  immutable.this.Nil.::[Int](x$1)
};