Posted on Feb 14, 2021

Write good PHP - Lookup-arrays

#php #programming #webdev

You have a list of potential values to return, dependent on a value to evaluate. A super common operation, right? You'll instantly think, chuck in an if statement, or even a switch, and call it a day - let's see an example. We want to return the relatives name based on the relation (Does anyone else forget names easily??):

$relative = $_GET['relative'];

if($relative == 'mother') {
    return 'Harriet';
}

if($relative == 'father') {
    return 'Robert';
}

if($relative == 'daughter') {
    return 'Rachel';
}

if($relative == 'grandmother') {
    return 'Audrey';
}

// imagine 10 more!

This is a perfectly adequate solution: but you'd probably want to use a switch, to simplify it even further:

$relative = $_GET['relative'];

switch ($relative) {
    case 'mother':
        return 'Harriet';
        break;
    case 'father':
        return 'Robert';
        break;
    case 'daughter':
        return 'Rachel';
        break;
    case 'grandmother':
        return 'Audrey';
        break;
    default:
        return 'relative not found!';
}

Great, this feels much more structured, but it's quite heavy on syntax, right? Perfectly serviceable, but let's take it one step further.

Enter lookup-arrays. A lookup array is a key-value paired list, where the key is what is looked up!

The above, in the form of a lookup-array is:

$relative = $_GET['relative'];

$relatives = [
    'mother' => 'Harriet',
    'father' => 'Robert',
    'daughter' => 'Rachel',
    'grandmother' => 'Audrey',
];

return $relatives[$relative] ?? 'relative not found!';

You can see how much easier to read a lookup-array is, and how it dramatically reduces the quantity of code, in a concise way! To note, lookup-arrays aren't always the best choice, but when they are, it should feel pretty natural!

Thanks for reading - let me know your thoughts!

Top comments (7)

Michal Král • Feb 15 '21 • Edited

Since PHP 8.0 you can use match expression.

return match( $_GET['relative'] ) {
        'mother' => 'Harriet',
        'father' => 'Robert',
        'daughter' => 'Rachel',
        'grandmother' => 'Audrey',
        'default' => 'relative not found!'
    };

Joe 🏴󠁧󠁢󠁷󠁬󠁳󠁿 • Feb 15 '21 • Edited

I love the match expression. Such a shame that so many existing codebases are stuck with older versions PHP.

I'd always opt for Match in PHP 8 😊

Ben Sinclair • Feb 15 '21

I'd never heard of it. It looks better than switch for most things, but oh dear the syntax is horrid with those arrows. It makes it look like it should be an associative array.

Michal Král • Feb 15 '21

BTW one key difference between match and switch is that match uses strict comparison whether switch doest not

Ben Sinclair • Feb 15 '21

You've made the switch version look more verbose by changing return to echo, meaning it's no longer the same code as in the first example. If you were refactoring the first, you'd do:

$relative = $_GET['relative'];

switch ($relative) {
    case 'mother':
        return 'Harriet';
    case 'father':
        return 'Robert';
    case 'daughter':
        return 'Rachel';
    case 'grandmother':
        return 'Audrey';
}