A Tour of Scala: Operators

Any method which takes a single parameter can be used as an infix operator in Scala. Here is the definition of classMyBool which defines three methods and, or, and negate.

class MyBool(x: Boolean) {
  def and(that: MyBool): MyBool = if (x) that else this
  def or(that: MyBool): MyBool = if (x) this else that
  def negate: MyBool = new MyBool(!x)
}

It is now possible to use and and or as infix operators:

def not(x: MyBool) = x negate; // semicolon required here
def xor(x: MyBool, y: MyBool) = (x or y) and not(x and y)

As the first line of this code shows, it is also possible to use nullary methods as postfix operators. The second line defines an xor function using the and and or methods as well as the new not function. In this example the use of infix operators helps to make the definition of xor more readable.

Here is the corresponding code in a more traditional object-oriented programming language syntax:

def not(x: MyBool) = x.negate; // semicolon required here
def xor(x: MyBool, y: MyBool) = x.or(y).and(x.and(y).negate)