Strange precedence of operators >>= and >>

Question

Having:

case class A(x: Int) {
  def >>= (y: A) = A(x * y.x)
  def >> (y: A) = A(x + y.x)
}

Since >>= and >> both start with >, they should have the same precedence and left associativity.

However:

A(5) >>= A(3) >> A(2)

returns 25.

But should return 17, because:

A(5) >>= A(3) >> A(2) == (A(5) >>= A(3)) >> A(2) == 17

It looks like Scala compiler puts parantheses in the wrong place.

Bug?

I think all characters are considered, not just the first. – Gábor Bakos Dec 08 '14 at 13:17 — Gábor Bakos, Dec 08 '14 at 13:17

score 7 · Accepted Answer · edited May 23 '17 at 10:33

7

As this comment explains: operators which end with a = but don't start with one are considered assignment operators. They get the lowest precedence. This rule is needed for operators such as += and *=.

edited May 23 '17 at 10:33

Community

1
1

answered Dec 08 '14 at 13:24

Jasper-M

14,966
2
26
37

But these operators have nothing to do with assignment! – ZhekaKozlov Dec 08 '14 at 13:27
But they look like assignments. With mutable datastructures, for instance: `val list = ListBuffer.empty[Int]; list += 3` But I agree that Scala's precedence policy is not optimal :) – Jasper-M Dec 08 '14 at 13:36

Strange precedence of operators >>= and >>

1 Answers1