Does Swift have any built-in reverse function for a Bool?

Question

The following extension works, yet I was wondering if Swift has any out of the box function that does such reverse. I already command clicked on Bool and it doesn't have anything reverse like nor I saw anything in the Documentation.

var x = true

extension Bool{
    mutating func reverse() -> Bool{
        if self == true {
            self = false
            return self
        } else {
          self = true
          return self
        }
    }
}

print(x.reverse()) // false

Answer 1

! is the "logical not" operator:

var x = true
x = !x
print(x) // false

In Swift 3 this operator is defined as a static function of the Bool type:

public struct Bool {

    // ...

    /// Performs a logical NOT operation on a Boolean value.
    ///
    /// The logical NOT operator (`!`) inverts a Boolean value. If the value is
    /// `true`, the result of the operation is `false`; if the value is `false`,
    /// the result is `true`.
    ///
    ///     var printedMessage = false
    ///
    ///     if !printedMessage {
    ///         print("You look nice today!")
    ///         printedMessage = true
    ///     }
    ///     // Prints "You look nice today!"
    ///
    /// - Parameter a: The Boolean value to negate.
    prefix public static func !(a: Bool) -> Bool

   // ...
}

There is no built-in mutating method which negates a boolean, but you can implement it using the ! operator:

extension Bool {
    mutating func negate() {
        self = !self
    }
}

var x = true
x.negate()
print(x) // false

Note that in Swift, mutating methods usually do not return the new value (compare sort() vs. sorted() for arrays).

---

Update: The proprosal

• SE-0199 Adding toggle to Bool

has been accepted, and a future version of Swift will have a toggle() method in the standard library:

extension Bool {
  /// Equivalent to `someBool = !someBool`
  ///
  /// Useful when operating on long chains:
  ///
  ///    myVar.prop1.prop2.enabled.toggle()
  mutating func toggle() {
    self = !self
  }
}