PHP Asymmetric Property Visibility in PHP 8.4

Asymmetric visibility, introduced in PHP 8.4, can make a property publicly readable but privately or protectedly writable.

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

How PHP Asymmetric Property Visibility in PHP 8.4 Works

Asymmetric visibility, introduced in PHP 8.4, can make a property publicly readable but privately or protectedly writable.

Compatibility note: Requires PHP 8.4 or later.

Example 1: Basic Usage

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

<?php

class Task { public private(set) string $status = "new"; public function complete(): void { $this->status = "done"; } }
$task = new Task();
$task->complete();
echo $task->status;

Output:

done

Asymmetric visibility, introduced in PHP 8.4, can make a property publicly readable but privately or protectedly writable.

Example 2: A Different Input

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

<?php

class Account { public protected(set) int $balance = 0; public function deposit(int $amount): void { $this->balance += $amount; } }
$account = new Account();
$account->deposit(50);
echo $account->balance;

Output:

50

Write visibility must not exceed read visibility; access from outside the allowed setter scope fails.

Practical Example: Applying the Feature

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

<?php

final class Document { public private(set) string $title; public function __construct(string $title) { $this->title = $title; } }
echo (new Document("Guide"))->title;

Output:

Guide

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

Important Behavior and Edge Cases

• Write visibility must not exceed read visibility; access from outside the allowed setter scope fails.
• Asymmetric visibility, introduced in PHP 8.4, can make a property publicly readable but privately or protectedly writable.
• Observe differences in empty inputs, invalid states and optional extension availability where relevant.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• Asymmetric visibility, introduced in PHP 8.4, can make a property publicly readable but privately or protectedly writable.
• Write visibility must not exceed read visibility; access from outside the allowed setter scope fails.
• Use the example that matches the values, runtime version and dependencies in your application.

PHP Asymmetric Property Visibility in PHP 8.4 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.