PHP WeakMap Explained with a Practical Example

WeakMap stores metadata keyed by objects without extending their lifetime solely through the map.

What It Does

WeakMap stores metadata keyed by objects without extending their lifetime solely through the map. The following examples distinguish a normal use case, a boundary case and a practical application.

Requirements and Compatibility

PHP 8.0 or later and object instances as WeakMap keys.

The code focuses on the core concept. Production implementation may also need routes, validation, persistence, authorization or deployment tooling.

Example 1: Basic Behavior

Start with the smallest meaningful working case.

<?php
$metadata = new WeakMap(); $object = new stdClass(); $metadata[$object] = ['hits' => 1];
echo $metadata[$object]['hits'];

Example 2: Another Case

Examine the edge case and the observable result.

<?php
$map = new WeakMap(); $key = new stdClass(); $map[$key] = 'temporary';
unset($key); gc_collect_cycles(); echo count($map);

Practical Example: Putting It to Use

Apply the technique to a small practical task.

<?php
$item = new stdClass(); $reference = WeakReference::create($item);
var_dump($reference->get() === $item);
unset($item); gc_collect_cycles(); var_dump($reference->get());

Important Behavior and Edge Cases

Do not depend on exact garbage-collection timing; keys vanish when no strong references remain.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• WeakMap stores metadata keyed by objects without extending their lifetime solely through the map.
• Do not depend on exact garbage-collection timing; keys vanish when no strong references remain.
• SplObjectStorage retains object keys strongly instead of weakly.

Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.