5 guidelines for coding with Booleans

operate saveUser(
  person: Person,
  emailOption: WelcomeEmailOption,
  verificationStatus: VerificationStatus
): void {
  if (emailOption === WelcomeEmailOption.Ship) {
    sendEmail(person.e-mail, 'Welcome!');
  }
  if (verificationStatus === VerificationStatus.Verified) {
    person.verified = true;
  }
  // save person to database...
}

And you may name it like this:

saveUser(newUser, WelcomeEmailOption.Ship, VerificationStatus.Unverified); 

Isn’t that so much simpler in your mind? That decision reads like documentation. It’s clear and to the purpose, and the maintainer can see instantly what the decision does and what the parameters imply. 

Booleans are a entice for future complexity

A bonus of enums is they’re expandable. Think about you could have a meals and beverage system that has small and enormous sized drinks. You would possibly find yourself with

var IsSmallDrink: boolean;

And also you construct your system round that Boolean variable, even having Boolean fields within the database for that data. However then the boss comes alongside and says, “Hey, we’re going to begin promoting medium drinks!”

Uh oh, that is going to be a serious change. All of a sudden, a easy Boolean has grow to be a legal responsibility. However when you had prevented Booleans and began with

enum DrinkSize {
  Small,
  Massive
}

Then including one other drink dimension turns into a lot simpler.

Look, Booleans are highly effective and easy. I’m sufficiently old to recollect when languages didn’t even have Boolean sorts. We needed to simulate them with integers:

10 LET FLAG = 0
20 IF FLAG = 1 THEN PRINT "YOU WILL NEVER SEE THIS"
30 LET FLAG = 1
40 IF FLAG = 1 THEN PRINT "NOW IT PRINTS"
50 END

So I perceive their attraction. However utilizing Booleans finally ends up being fraught with peril. Are there exceptions? Certain, there are easy circumstances the place issues truly are and all the time will likely be both true or false—like isLoading. However in case you are in a rush, otherwise you let your guard down, or perhaps you are feeling a bit lazy, you may simply fall into the entice of writing convoluted, hard-to-reason-about code. So tread evenly and punctiliously earlier than utilizing a Boolean variable.