!0 is false in rails. Why? [closed]

Question

I just got through a troubling bug in my rails application and I discovered that the problem was that !0 was false. I was assuming that, that should be true.

I was under the impression that ! operator would reverse the bits in an integer so 0 would become all 1's and hence would be true.

That is not the case, why?

Also note from the rails console:

1.9.3p286 :002 > !0
 => false 
1.9.3p286 :003 > 0
 => 0 
1.9.3p286 :004 > !1
 => false 
1.9.3p286 :005 > !!0
 => true 
1.9.3p286 :006 > !0
 => false 
1.9.3p286 :007 > !23
 => false 

Answer 1

Because 0 is not equivalent to false. 0 is an integer value and the boolean value of all integers is true. The only things that evaluate to false are nil and, explicitly, false.

Given that 0 is true, !0 is, intuitively, false.

! is not a bit-wise operator, it is a logical NOT. Perhaps you meant ~0?

Answer 2

In ruby there are only two values that evaluate to false in logical expressions: false and nil. Since 0 is neither of them, it evaluates to true and thus !true equals false.

Answer 3

From this blog

Most objects in Ruby will have a boolean value of true. Only two objects have a boolean value of false, these are the false object itself and the nil object.

So any integer (even 0) has a boolean value true. And thus !0 evaluates to false