New Features in PHP 8.3: Typed Class Constants, Dynamic Class Constants, Readonly Property Deep Clone, and json_validate() Function

PHP 8.3 has been officially released, and the active support period for PHP 8.0 has already ended; security support for PHP 8.0 will cease three days after the PHP 8.3 release, on 2023‑11‑26.

The main new features of PHP 8.3 are:

Typed class constants

// PHP < 8.3
interface I {
    // We may naively assume that the PHP constant is always a string.
    const PHP = 'PHP 8.2';
}

class Foo implements I {
    // But implementing classes may define it as an array.
    const PHP = [];
}

// PHP 8.3
interface I {
    const string PHP = 'PHP 8.3';
}

class Foo implements I {
    const string PHP = [];
}
// Fatal error: Cannot use array as value for class constant Foo::PHP of type string

Dynamic retrieval of class constants

// PHP < 8.3
class Foo {
    const PHP = 'PHP 8.2';
}

$searchableConstant = 'PHP';
var_dump(constant(Foo::class . "::{$searchableConstant}"));

// PHP 8.3
class Foo {
    const PHP = 'PHP 8.3';
}

$searchableConstant = 'PHP';
var_dump(Foo::{$searchableConstant});

Readonly property deep clone

The readonly attribute can now be modified once inside the magic __clone method, enabling deep cloning of readonly properties.

// PHP < 8.3
class PHP {
    public string $version = '8.2';
}

readonly class Foo {
    public function __construct(public PHP $php) {}
    public function __clone(): void {
        $this->php = clone $this->php;
    }
}

$instance = new Foo(new PHP());
$cloned = clone $instance;
// Fatal error: Cannot modify readonly property Foo::$php

// PHP 8.3
class PHP {
    public string $version = '8.2';
}

readonly class Foo {
    public function __construct(public PHP $php) {}
    public function __clone(): void {
        $this->php = clone $this->php;
    }
}

$instance = new Foo(new PHP());
$cloned = clone $instance;
$cloned->php->version = '8.3';

New json_validate() function

The json_validate() function checks whether a string is syntactically valid JSON more efficiently than using json_decode() followed by error checking.

// PHP < 8.3
function json_validate(string $string): bool {
    json_decode($string);
    return json_last_error() === JSON_ERROR_NONE;
}
var_dump(json_validate('{ "test": { "foo": "bar" } }')); // true

// PHP 8.3
var_dump(json_validate('{ "test": { "foo": "bar" } }')); // true

For more details, refer to the official release notes: https://www.php.net/releases/8.3/en.php

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