Overload the '!' Logical NOT Operator for Custom Swift Types

Written by Team Kodeco

The ! operator in Swift is used for performing a logical NOT operation, which reverses the truth value of a Boolean. When working with custom types in Swift, you may want to overload the ! operator to perform a similar operation specific to your custom type.

To overload the ! operator in Swift, you’ll need to define a function called ! with no parameters and the operator keyword before the function name. Here’s an example of how you might overload the ! operator for a custom LightSwitch class:

class LightSwitch {
  var on: Bool
  init(on: Bool) {
    self.on = on
  }
  static prefix func ! (lightSwitch: LightSwitch) -> LightSwitch {
    return LightSwitch(on: !lightSwitch.on)
  }
}

In this example, you define a LightSwitch class with an on property indicating whether the switch is on or off. You then define an operator function as a prefix function that takes a LightSwitch as parameter and returns a new LightSwitch instance with the opposite value of the on property.

Now you can use the ! operator to toggle the on/off state of a LightSwitch instance:

var lightSwitch = LightSwitch(on: true)
print(lightSwitch.on) // true
lightSwitch = !lightSwitch
print(lightSwitch.on) // false