Why would you use a !! operator

I came across abit of ruby in a example

def role?(role)
  return !!self.roles.find_by_name(role.to_s.camelize)
end

Why would you ever use !!? Is it not the same开发者_Go百科 as

 return self.roles.find_by_name(role.to_s.camelize)

Does adding the double exclamation mark add something to the evaluation?

You use it if you only want the boolean, not the object. Any non-nil object except for boolean false represents true, however, you'd return the data as well. By double negating it, you return a proper boolean.

Disclaimer: Not a ruby programmer but having a stab at this.

!!, double bang or "not not", might convert the value to a boolean. One ! returns the boolean opposite and another bang thereafter will flip it to its normal boolean value.

This is a double negation which results in a boolean:

irb(main):016:0> !1
=> false
irb(main):013:0> !0
=> false
irb(main):014:0> !nil
=> true
irb(main):015:0> !!nil
=> false

Yes in your case you can be sure that the function is returning only true or false. If you would omit !! you would return a list of roles

with this little trick you get the actual boolean value of an expression, e.g.:

!! 3 
=> true

!! nil
 => false 

!! 0
 => true 

In Ruby anything that isn't nil or false , is true!

In your example code this trick makes sure that you never return anything else
but true or false

If you would omit the !! , you would return the list of roles, or nil