Logical Operators

Ruby has three logical operators, && (AND), || (OR), and ! (NOT). && evaluates to true if both its operands are true. || evaluates to true if at least one operand is true. ! returns true if its operand is false and true if its operand is false.

In true || false, the Ruby interpreter doesn't evaluate the code after || because it's irrelevant. Since the first operand is true, the expression will be true regardless of the second operand. This behavior is an example of short-circuit evaluation, where the second operand of a logical operator is evaluated only if the first operand does not suffice to determine the value of the expression. Conversely, false && true is also an example of short-circuiting (the expression will be false regardless of the second operand).

!, sometimes known as bang, reverses the boolean value of its operand. Though ! receives a single operand, that operand can be the result of an expression. !(false || true) returns false. !false || true would return true and would short-circuit.

&& and || also permit expressions as operands: