Maxi ContieriThis handy operator is a trouble maker.
TL;DR: Don't mix booleans with non-booleans.
Problems
Not Declarative Code
Hard to debug
Magic Castings
Accidental Complexity
Solutions
Be Explicit
Don't mix Booleans with non-booleans.
Be Smarter than your compiler.
Stay loyal to the bijection.
Sample Code
Wrong
!true // returns false
!false // returns true
isActive = true
!isActive // returns false
age = 54
!age // returns false
array = []
!array // returns false
obj = new Object;
!obj // returns false
!!true // returns true
!!false // returns false
!!isActive // returns true
!!age // returns true
!!array // returns true
!!obj // returns true
Right
!true // returns false
!false // returns true
isActive = true
!isActive // returns false
age = 54
!age // should return type mismatch (or 54 factorial!)
array = []
!array // should return type mismatch
obj = new Object;
!obj // should return type mismatch (what is an obejct negated in a real domain?)
!!true // returns true - it is idempotent
!!false // returns false - it is idempotent
!!isActive // returns true - it is idempotent
!!age // nonsense
!!array // nonsense
!!obj // nonsense
Detection
Since this is a "feature" in some languages it would be hard to test. We can set programming policies or choose more strict languages.
We should detect ! !! usages in non-boolean objects and warn our programmers.
Tags
Casting
Coercion
Javascript
Conclusion
Languages like JavaScript divide their whole universe into true or false values. This decision hides errors when dealing with non booleans.
We should be very strict and keep booleans (and their behavior), far away from non booleans.
Relations
More info
Credits
Photo by Greg Rakozy on Unsplash
It is easier to write an incorrect program than understand a correct one.
Alan J Perlis
