It’s not uncommon to see people try and equate PHP’s arrays to similar features in other programming languages, as PHP has a bit of a unique approach by using a single data structure for both ordered lists and key-value objects.
Some common comparisons include:
- PHP ordered array: Python lists, JavaScript arrays, Ruby arrays
- PHP associative array: Python dictionaries, JavaScript objects, Ruby hashes
However, because both of these concepts are a single data structure in PHP, that adds an oft-overlooked feature for newcomers to the language:
Associative arrays in PHP are predictably ordered.
Let’s look at an example, a simple real-world use case; a navigation menu.
// The order of the items in the source code determine
// the order they will be shown on the rendered page:
$navigation = [
'/' => 'Home',
'/blog' => 'Blog',
'/about' => 'About us',
'/contact' => 'Get in touch!',
];
// We can iterate over them like any ordered list:
foreach ($navigation as $link => $text) {
echo "<a href=\"{$link}\">{$text}</a>\n";
}
// The output is always predictable:
// <a href="/">Home</a>
// <a href="/blog">Blog</a>
// <a href="/about">About us</a>
// <a href="/contact">Get in touch!</a>
Most languages allow iterating over key-value data structures, but they’re not always guaranteed to be ordered like PHP’s are. For example, the Lua programming language has a table data structure that can be used for both ordered lists and key-value objects, but the order of the string keys in a table are not guaranteed.
If you ever add a new key to the array, such as by defining $navigation['/services'] = 'Our services';, it will always be added to the end of the list when you iterate over the array. If you need to prepend a key to an associative array, you can do that too.