Scala maps -> operator

Question

What does the symbol -> mean in the context of a Map in Scala?

Scala’s Predef class offers an implicit conversion that lets

Answer 1

Here's the implicit conversion:

implicit def any2ArrowAssoc[A](x: A): ArrowAssoc[A] = new ArrowAssoc(x)

This will convert any type into an instance of "ArrowAssoc"

class ArrowAssoc[A](x: A) {
    def -> [B](y: B): Tuple2[A, B] = Tuple2(x, y)
}

So when Scala sees

"a"->1

It says "There is no method named '->' on String. Are there any implicit conversions in scope that can give me a type that has a method named '->'?" Predef.scala is automatically in scope, and offers a conversion to ArrowAssoc, which obviously has the '->' method. Scala then essentially converts the above to

any2ArrowAssoc("a").->(1)

This method returns a Tuple2("a", 1) (often called a Pair). Map has a constructor that thats an array (varargs) of Tuple2s, so we're off to races! No magic in the compiler (besides implicit conversion, which is used extensively and for many different purposes), and no magic in Maps constructor.