# First XOR

#PHP
#logic

I've been writing PHP for over 15 years at this point, and not once have I ever had a need to use the logical `{php}xor`
operator, until now!

It came up while writing a feature which matched email addresses from an `email_logs` table to the `users` table, in
this app there were two types of users, admins and customers; they're stored in different tables.

The naive approach would be to try one and then the other:

```php
$user = CustomerUser::query()
    ->where('email', $log->getToAddress())
    ->first();

$user ??= AdminUser::query()
    ->where('email', $log->getToAddress())
    ->first();
```

There's a problem with this approach. What if an email address appears in both the `AdminUser` table and the 
`CustomerUser` table? This wasn't just theoretical, this was something we actually needed to consider. Enter the
`{php}xor`:

```php
$customerUser = CustomerUser::query()
    ->where('email', $log->getToAddress())
    ->first();

$adminUser = AdminUser::query()
    ->where('email', $log->getToAddress())
    ->first();

if ($customerUser === null xor $adminUser === null) {
    $user = $customerUser ?? $adminUser;
}
```