PHP RFC: Remove PHP 4 Constructors
- Version: 1.0
- Date: 2014-11-17
- Author: Levi Morrison levim@php.net
- Contributors: Andrea Faulds ajf@ajf.me
- Status: Deprecation Implemented (in PHP 7.0)
- First Published at: http://wiki.php.net/rfc/remove_php4_constructors
Introduction
PHP 4 constructors are methods that have the same name as the class they are defined in. PHP 5 preserved the ability to use PHP 4 style constructors in some cases; the strangeness of when the constructor is and isn't used increases the mental model for programmers.
class Filter { // A constructor in PHP 4 and 5 function filter($a) {} }
// Namespaced classes do not recognize PHP 4 constructors namespace NS; class Filter { // Not a constructor function filter($a) {} }
// Defining __construct and filter makes filter a normal method class Filter { function __construct() {} // Not a constructor function filter($a) {} } //But defining filter first raises an E_STRICT class Filter { // Not a constructor… function filter($a) {} // This raises E_STRICT function __construct() {} }
Proposal
PHP 7 will emit E_DEPRECATED whenever a PHP 4 constructor is defined. When the method name matches the class name, the class is not in a namespace, and a PHP 5 constructor (__construct) is not present then an E_DEPRECATED will be emitted. PHP 8 will stop emitting E_DEPRECATED and the methods will not be recognized as constructors.
PHP 7 will also stop emitting E_STRICT when a method with the same name as the class is present as well as __construct.
Refer to the Examples section to see how code is impacted.
Backward Incompatible Changes
Since an E_DEPRECATED will be emitted in PHP 7 there may be some backwards compatibility breaks when people use custom error handlers.
In PHP 8 recognition for old constructors will be outright removed, meaning that anything without a __construct will not work the same way it used to. The old-style constructor will be considered a normal method and will not be called when the object is constructed. The fix is to rename the constructor to __construct.
Examples
class Filter { // PHP 5: filter is a constructor // PHP 7: filter is a constructor and E_DEPRECATED is raised // PHP 8: filter is a normal method and is not a constructor; no E_DEPRECATED is raised function filter($a) {} } $filter = new ReflectionMethod('Filter', 'filter'); // PHP 5: bool(true) // PHP 7: bool(true) // PHP 8: bool(false) var_dump($filter->isConstructor());
// function filter is not used as constructor in PHP 5+ class Filter { // PHP 5: E_STRICT "Redefining already defined constructor" // PHP 7: No error is raised // PHP 8: No error is raised function filter($a) {} function __construct() {} }
// function filter is not used as constructor in PHP 5+ class Filter { function __construct() {} // PHP 5.0.0 - 5.2.13, 5.3.0 - 5.3.2: E_STRICT "Redefining already defined constructor" // PHP 5.2.14 - 5.2.17, 5.3.3 - 5.6: No error is raised // PHP 7: No error is raised // PHP 8: No error is raised function filter($a) {} }
class Filter { // PHP 5: filter is a constructor // PHP 7: filter is a constructor and E_DEPRECATED is raised // PHP 8: filter is a normal method and is not a constructor; no E_DEPRECATED is raised function filter() {} } class FilterX extends Filter { function __construct() { // PHP 5: Filter::filter is called; no error // PHP 7: Filter::filter is called; no error // PHP 8: "Fatal error: Cannot call constructor" parent::__construct(); } } new FilterX();
Voting
This RFC targets PHP 7 and PHP 8. Please read the RFC to understand what is being proposed.
This RFC requires 2/3 vote in favor of deprecating and removing PHP 4 style constructors to pass.
Do you vote to remove PHP 4 constructors as outlined in this RFC?
Voting will close on the evening (UTC-7) of March 6th.
Patches and Tests
An implementation based on the master branch can be found here: https://github.com/php/php-src/pull/1061