ruby - Bang (!) at the beginning of method name

Question

What is the purpose of the exclamation mark right before the taking_damage method in this example of code?

if warrior.health < 20 && !taking_damage?(warrior)
     warrior.rest!
end

Answer 1

It is the boolean operation Negation and thus equivalent to the Ruby keyword not.

You can read the line like this:

“If the warrior's health is below 20 and the warrior is NOT taking damage then the warrior must rest.”</p>

Answer 2

It is the negation operator which takes the method/variable's truthiness and returns the opposite of it.

Answer 3

此运算符还可用于将任何值转换为真假（布尔值）。这是一个例子：

 > !nil
 => true 
 > !!nil
 => false