It doesn't really work quite as you suggest; it's just that a &! b == a & !b where !b is true if b is nil or false, and false otherwise. & works as a bit

It doesn't really work quite as you suggest; it's just that a &! b == a & !b where !b is true if b is nil or false, and false otherwise. & works as a bitwise AND for numbers, and a logical AND for boolean values. You can't mix the two, but as long as a is a boolean, you'll get some kind of result out of the calculation: true &! true # => false true &! false # => true true &! 0 # => false 0 &! 0 # => TypeError: can't convert false into Integer