The logical, !, operator is a prefix operator that negates, or reverses, the Boolean value of its operand. It returns false when the operand is true, and returns true, when the operand is false.

Note that unlike the && and || operators, the ! operator acts on a single value.

Assume we have the following variables that hold Boolean values.

let a = true
let b = false

Prepending the ! operator to both values will result in the opposite Boolean:

print(!a) // Prints: false 
print(!b) // Prints: true 

The ! operator can also be used to negate the value of an expression as long as that expression is contained within parentheses. The following example first executes the logic within the parentheses and then negates it.

print(!(true && false)) // Prints: true 

The resulting value will be true since true && false results in false and !false is true.