What does !!some_object do?

Question

Possible Duplicate:
What does !! mean in ruby?

what is this function doing?

def current_product?
   !!current_product
end

Isn't that a double negative?

Duplicate of [What does !! mean in ruby?](http://stackoverflow.com/questions/524658/what-does-mean-in-ruby). — Andrew Grimm, Dec 09 '10 at 02:07

score 5 · Accepted Answer · answered Dec 09 '10 at 02:03

5

!! is basically a cast to boolean. If current_product is truthy, !current_product is false and !!current_product is true, and vice versa. I.e. it converts truthy values to true and falsy values to false.

answered Dec 09 '10 at 02:03

deceze

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score 1 · Answer 2 · edited May 23 '17 at 12:04

1

It's effectively a cast/conversion to boolean.

Similar question, but for C++: Doube Negation in C++ code

Also a pretty decent post about it here: !! (The double bang / double not) in Ruby

edited May 23 '17 at 12:04

Community

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answered Dec 09 '10 at 02:02

eldarerathis

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score 1 · Answer 3 · answered Dec 09 '10 at 02:06

This is a pattern you'll see in any language where every object has a truth value, but there are canonical booleans (whether they be called True and False, 1 and 0, 1 and "", t and nil, whatever). !!x is essentially a "cast to boolean", in that !!x has the same truth-value as x, but !!x will always be one of the canonical true/false values, instead of any old true/false value.

What does !!some_object do?

3 Answers3