PHP Closures: Capturing Variables by Value and Reference

Capturing by value snapshots a variable, while capturing by reference observes and can mutate the same outside variable.

The examples below begin with the core behavior, then move to an application-oriented use.

How PHP Closures: Capturing Variables by Value and Reference Works

Capturing by value snapshots a variable, while capturing by reference observes and can mutate the same outside variable.

Example 1: Basic Usage

This example uses a small input to make the main behavior visible.

<?php

$status = "draft";
$byValue = function () use ($status): string { return $status; };
$status = "published";
echo $byValue();

Output:

draft

Capturing by value snapshots a variable, while capturing by reference observes and can mutate the same outside variable.

Example 2: A Different Input

A different set of values shows the same operation in another situation.

<?php

$status = "draft";
$byReference = function () use (&$status): string { return $status; };
$status = "published";
echo $byReference();

Output:

published

Reference capture introduces shared mutable state, so avoid it unless the callback truly needs to update external state.

Practical Example: Applying the Feature

This example shows an application-style use of the feature, with its surrounding setup visible.

<?php

$counter = 2;
$byValue = function () use ($counter): int { return $counter; };
$byReference = function () use (&$counter): int { return $counter; };
$counter = 8;
echo $byValue() . ":" . $byReference();

Output:

2:8

The code is shown for learning. Adjust the class names, inputs and error handling to suit your application.

Important Behavior and Edge Cases

• Reference capture introduces shared mutable state, so avoid it unless the callback truly needs to update external state.
• Capturing by value snapshots a variable, while capturing by reference observes and can mutate the same outside variable.
• Observe differences in empty inputs, invalid states and optional extension availability where relevant.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• Capturing by value snapshots a variable, while capturing by reference observes and can mutate the same outside variable.
• Reference capture introduces shared mutable state, so avoid it unless the callback truly needs to update external state.
• Use the example that matches the values, runtime version and dependencies in your application.

PHP Closures: Capturing Variables by Value and Reference is useful when its behavior matches the data structure and lifecycle of your PHP application. Choose it with a clear understanding of its preconditions and returned values.