PHP 8.3: What's New, Release History & Support Lifecycle

Typed Class Constants

Class, interface, trait, and enum constants can now declare explicit types. This ensures type consistency when constants are overridden or implemented, preventing subtle bugs.

In previous versions, type mismatches were silently allowed:

interface Example {
    const DATA = 'string value';
}

class Test implements Example {
    const DATA = []; // No error before PHP 8.3
}

PHP 8.3 enforces the declared type and throws an error on mismatch:

interface Example {
    const string DATA = 'PHP 8.3';
}

class Test implements Example {
    const string DATA = []; // Fatal error: Type mismatch
}

Dynamic Class Constant and Property Access

Accessing class constants dynamically is now simpler and more readable using a new syntax.

Old approach required string concatenation:

class Sample {
    const VERSION = '8.3';
}

$constName = 'VERSION';
var_dump(constant('Sample::' . $constName));

New cleaner syntax:

class Sample {
    const VERSION = '8.3';
}

$constName = 'VERSION';
var_dump(Sample::{$constName});

The same syntax also works for dynamic property access on objects.

The #[\Override] Attribute

This built-in attribute verifies that a method actually overrides a parent method or implements an interface method. It catches common typos at runtime.

Without the attribute, misspelled methods silently fail to override:

class Child extends Parent {
    public function saveData() { ... } // Typo: meant to be saveDate()
}

With the attribute, PHP throws an error if no matching parent method exists:

class Child extends Parent {
    #[\Override]
    public function saveData() { ... } // Error if no parent method matches
}

Deep Cloning of Readonly Objects

Readonly properties can now be reassigned inside the __clone() method, enabling proper deep cloning of objects with readonly data.

readonly class Config {
    public function __construct(public Database $db) {}

    public function __clone(): void {
        $this->db = clone $this->db; // Allowed in PHP 8.3
    }
}

New json_validate() Function

A lightweight function to check if a string is valid JSON without decoding it fully. It is faster and uses less memory than json_decode() when only validation is needed.

json_validate('{"name": "PHP", "version": 8.3}'); // true
json_validate('invalid json'); // false

Random Extension Improvements

The Random extension gains new methods for more flexible and unbiased random value generation:

• Random\Randomizer::getBytesFromString() - Generate random bytes using only characters from a provided string.
• Random\Randomizer::getFloat(), pickArrayValue(), and others for unbiased floating-point and array selection.

Command Line Linter Supports Multiple Files

The built-in linter can now check syntax for multiple files in one command:

php -l file1.php file2.php file3.php