# Where's My Logical XOR Operator?

Learn a simple trick to mimic XOR and XNOR boolean operators in your favorite language where it might be missing.

Many popular programming languages don’t have logical `XOR`

or `XNOR`

operators. ^{1} Because of this, it may not be clear how to check scenarios such as:

- Either one of
`A`

or`B`

hold true, but**not both**. - Either both
`A`

and`B`

hold true, or are both false, but**not either one of them individually**.

In case you’re unfamiliar with boolean logic, note that those scenarios are equivalent to:

`A XOR B`

`A XNOR B`

Without `XOR`

or `XNOR`

, you may be tempted to write code this way:

// A XOR B (A || B) && !(A && B) // A XNOR B (!A && !B) || (A && B)

…which could work, with lots of head scratching and unit testing…

Until you realize that it can be simplified *greatly* into:

// A XOR B A !== B // A XNOR B A === B

Super elegant, isn’t it? 🪄

## How does this trick work?

Observe that we’re checking equality between boolean^{2} values, so the truth tables look something like this:

// XOR false !== false // => false false !== true // => true true !== false // => true true !== true // => false // XNOR false === false // => true false === true // => false true === false // => false true === true // => true

The key insight is that if the two conditions are different, then *one and only one of them must be true*, which gives you the `XOR`

condition. Inverting it trivially gives you `XNOR`

.

## Is it useful?

Admittedly, it’s probably not that useful in everyday programming. It’s very rare to have to check for a `XOR`

condition in real life (it might even be a code smell). I would have come up with a fun Christmas example if I could think of one, but I really couldn’t.

Hey now — at least you can do part 2 of day 2 of Advent of Code 2020 without having to write a bunch of boolean spaghetti ✌

## Footnotes:

^{1}

Your favorite programming language may have *bitwise* `XOR`

or `XNOR`

operators though, but they’re not directly useful for checking conditionals, since they work on bits (i.e. 1s and 0s) instead of boolean values (i.e. `true`

and `false`

).

^{2}

And they *must* be boolean values, otherwise it may break. In JavaScript and TypeScript, you can force values to be boolean using `!`

and `!!`

.