PHP WeakMap::offsetSet() Method: Usage and Examples

Adds or updates metadata for an object key without retaining it strongly.

The examples focus on the operation itself, including the important distinction: SplObjectStorage, unlike WeakMap, retains strong object references.

What It Does

Use the examples below to observe the behavior on a small dataset before extending it to application code.

Syntax and Return Value

WeakMap::offsetSet($object, mixed $value): void

The displayed signature describes the API or identifies any correction or optional dependency. When a parameter is optional, supply it only when the task requires it.

Parameters

• object: required.
• value: required.

Declared return type: void. Read the behavior notes for important cases such as empty collections and destructive iteration.

Example 1: Basic Use

The map tracks an object only while another strong reference keeps it alive; keys use identity rather than a name string.

<?php
$user = (object) ["name" => 'Ari'];
$other = (object) ["name" => "guest"];
$metadata = new WeakMap();
$metadata[$user] = ["score" => 2];
$metadata->offsetSet($other, ["score" => 9]);
echo count($metadata);

Output from a successful local PHP 8.4 run:

2

Example 2: Checking Behavior

The map tracks an object only while another strong reference keeps it alive; keys use identity rather than a name string.

<?php
$user = (object) ["name" => 'Bo'];
$other = (object) ["name" => "guest"];
$metadata = new WeakMap();
$metadata[$user] = ["score" => 3];
$metadata->offsetSet($other, ["score" => 9]);
echo count($metadata);

Output from a successful local PHP 8.4 run:

2

Example 3: Practical Example

The map tracks an object only while another strong reference keeps it alive; keys use identity rather than a name string.

<?php
$user = (object) ["name" => 'Cam'];
$other = (object) ["name" => "guest"];
$metadata = new WeakMap();
$metadata[$user] = ["score" => 4];
$metadata->offsetSet($other, ["score" => 9]);
echo count($metadata);

Output from a successful local PHP 8.4 run:

2

Important Behavior and Edge Cases

The key must be an object; dropping all other references removes its entry.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Adds or updates metadata for an object key without retaining it strongly.
• The key must be an object; dropping all other references removes its entry.
• SplObjectStorage, unlike WeakMap, retains strong object references.

Use WeakMap::offsetSet when its documented behavior matches the problem. Test the relevant edge cases in your own runtime before deploying it.