What's the meaning of -> in scala

Question

When I read the book 《Functional Programming in scala》. I find the expression like this:

case (Cons(h, t), Empty) => 
    Some(f(Some(h()), Option.empty[B]) -> (t(), empty[B]))

What's the difference between

Some(f(Some(h()), Option.empty[B]), (t(), empty[B]))

Answer 1

If your 2nd example compiles, it should compile with a warning: creating a 2-tuple: this may not be what you want Otherwise it would fail because Some() doesn't take two parameters. The 1st example should compile because the -> is explicitly creating the tuple to send as a single parameter to the (outer) Some() .

When creating a tuple of two elements you have the option of using parentheses and comma (5, true) , or the arrow 5 -> true . In most situations the parentheses are optional when using the arrow version.

The arrow can't be used if you want more than 2 elements (ie not nested tuples):

'c' -> 'b' -> 'x'
//res0: ((Char, Char), Char) = ((c,b),x)

Answer 2

The -> is actually a method of the ArrowAssoc class to which every object can be implicitly converted. See the object scala.Predef . It is defined as:

def -> [B](y: B): Tuple2[A, B] = Tuple2(x, y)

This means that 1 -> 2 is equivalent to 1.->(2) which evaluates to Tuple2(1, 2) . This is also explained in section 21.4 of the book (3rd edition).