Problem!: In PHP, Null Coalescing Operator with Arrays Leads to Bugs!

Share

2024-11-13

One issue I had recently was that I wanted to try to get a value from an array in PHP, and if it didn't exist, I wanted to get a default value. Because I'm a very smart person, instead of spending 30 seconds programming this the obvious way, I spent 2 minutes Googling how to do it the "correct" way then another few minutes figuring out why things were suddenly not working anymore when I used a null coalescing operator (??).

Essentially, if you do this:

$value = $my_array['key'] ?? $default;

It looks like it does the same thing it does in Javascript:

const value = my_object['key'] ?? default;

But it doesn't.

Despite the similar syntax, what happens in PHP is different from what happens in Javascript when you use ??.

In PHP, if $my_array['key'] is undefined, $value will be $default. This makes sense and it's what we want.

HOWEVER, if $my_array is undefined, $value will also be $default, which is totally not what we want!

This means that if you spelled $my_array wrong, e.g. $my_arrya, PHP won't complain about it, and you'll be left wondering why your code is always using the default value even though you have set everything right.

In Javascript, my_object['key'] will error if my_object is undefined. The only thing that ?? does in Javascript is check if a value is null or undefined, it doesn't magically hide errors that would come from having undefined variables.

In Python, you can just do this:

value = my_dict.get('key', default_value)

By the way, the solution to solving this in PHP, if you really need to get a bunch of values, is to simply code your own default getter utility.

function get_array_key_or_default(array $array, string $key, mixed $default) {
    if(array_key_exists($key, $array)) {
        return $array[$key];
    } else {
        return $default;
    }
}

View Comments