This 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

1. Be Explicit

2. Don't mix Booleans with non-booleans.

3. Fail Fast

4. Be Smarter than your compiler.

5. Stay loyal to the bijection.

The One and Only Software Design Principle

Maxi Contieri ・ Oct 13 '20

#beginners #tutorial #design #oop

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

Code Smell 24 - Boolean Coercions

Maxi Contieri ・ Nov 14 '20

#oop #tutorial #boolean #coercion

Code Smell 06 - Too Clever Programmer

Maxi Contieri ・ Oct 25 '20

#codenewbie #tutorial #beginners

More info

Reddit

Double Bang

Mozilla

Credits

Photo by Greg Rakozy on Unsplash

It is easier to write an incorrect program than understand a correct one.

Alan J Perlis

Software Engineering Great Quotes

Maxi Contieri ・ Dec 28 '20

#codenewbie #programming #quotes #software