The final keyword has no other effect except to restrict inheritance. Members should not be given the final keyword.

[wheakerd]

Description

php version: 8.4.2
If it is possible to operate on non-public member properties of a class, it does not matter whether the member properties that are applied final have the final keyword or not.

class Example
{
    final protected mixed $value = 0;
}
$obj = new Example;
var_dump(
    (function () {
        $this->value += 1;
        return $this->value;
    })->call($obj)
);

// Output:
// int(1)

By promoting the scope, it is also possible to achieve the same behavior as a final method by accessing the attributes of the class.

class Database {
    private PDO $connection;

    final public function connect($host, $username, $password) {
        $this->connect = new PDO(... func_num_args());
    }
}

$db = new Database;
$db->connect('mysql:host=localhost;dbname=old_database;charset=utf8', 'username', 'password');

//	change database
(function () {
	$pdo = new PDO('mysql:host=localhost;dbname=new_database;charset=utf8', 'username', 'password');
	$this->connection = $pdo;
})->call($db)

Some built-in extensions require final classes to not allow inheritance, but they cannot avoid providing scopes to operate on internal members of the class.

[wheakerd]

But having the final keyword can improve performance, thanks to the jit compiler.
final class's private > final class's protected > final protected > private > protected

[damianwadley]

The final keyword has no other effect except to restrict inheritance.

I don't follow. "The final keyword prevents child classes from overriding a method, property, or constant" is literally its purpose for existing. Are you saying it should have some other, additional effects?

What bug/feature are you trying to report here?

[wheakerd]

@damianwadley What I mean is that even if the final keyword is added, it can still be manipulated externally. Then its existence is meaningless.

[wheakerd]

Even built-in classes provided by extensions are no exception. Can we use the AllowDynamicProperties approach to issue warnings?

[wheakerd]

@damianwadley Sorry, the previous documentation was missing $obj = new Example;, it is now included. 😂

[damianwadley]

final does not mean readonly or private. It means exactly what I quoted: a child class cannot override it with a new definition. None of your examples demonstrate this principle.

So I'll ask again: what bug are you trying to report? What output or error messages are you expecting to get?