PHP 8.0 Weak Map

This tutorial will guide you on how to use the Weak Map in PHP. The Weak Map is a crucial feature in PHP 8.0 that aids in writing optimized and memory-efficient code. In this tutorial, we will cover the basics of using the Weak Map class, including how to create a Weak Map, add and remove entries from a Weak Map, and iterate over the entries in a Weak Map.

What's a Weak Map?

A Weak Map is a specific type of data structure in PHP designed to store key-value pairs where keys are objects, and values can be any data type. Unlike traditional PHP arrays, weak map objects have no concrete reference to the object keys. So, if object keys have been garbage collected, they are automatically removed from the Weak Map, even if values are still associated with them.

How to Use Weak Map

To effectively utilize a Weak Map, you first need to create one. You can initialize a new Weak Map using the new WeakMap() constructor. After instantiation, you can populate the Weak Map with key-value pairs via the offsetSet() method. To get the value associated with a specific key, you can use the offsetGet() method.

Creating a Weak Map

To create a Weak Map, you can use the WeakMap class:

$weakMap = new WeakMap();

Adding Entries to a Weak Map

You can add key-value pairs like you do with regular arrays:

$object1 = new stdClass();
$object2 = new stdClass();

$weakMap[$object1] = "value1";
$weakMap[$object2] = "value2";

Accessing Values in a Weak Map

To access the value associated with an object, use the object as the key:

echo $weakMap[$object1]; // Outputs "value1"

Removing Entries from a Weak Map

With the Weak Map, entries get removed automatically when the object keys are garbage-collected.

unset($object1);
// Now $object1 is eligible for garbage collection.
// Once it's collected, its entry will be automatically removed from $weakMap.

Example of Caching Object Metadata Using Weak Map

Assume you have a User class and want to cache some metadata without affecting the lifecycle of each User object. Here's how you can do it with Weak Map:

class User {
    public $name;
    // ... other properties and methods
}

$metadataCache = new WeakMap();

$user1 = new User();
$user1->name = 'Alex';

// Cache metadata in WeakMap
$metadataCache[$user1] = ['lastLogin' => time()];

// Access the metadata
echo $metadataCache[$user1]['lastLogin']; // Outputs the last login time for Alex

In the above example, the metadata associated with the User objects will be automatically cleared when the objects are destroyed. This helps to prevent memory leaks and improves the performance of your code.

Conclusion

The WeakMap class is a powerful tool that can be used to improve your PHP code's memory efficiency and performance. If you are working with objects that you do not want to prevent from being garbage collected, then a Weak Map is an excellent option to consider.