Bug #61970 [Opn]: Restraining __construct() access level in subclass gives a fatal error
Edit report at https://bugs.php.net/bug.php?id=61970&edit=1
ID: 61970
Updated by: cataphract@php.net
Reported by: postmaster at greg0ire dot fr
Summary: Restraining __construct() access level in subclass
gives a fatal error
Status: Open
Type: Bug
Package: Class/Object related
Operating System: Linux
PHP Version: 5.3.12
Block user comment: N
Private report: N
New Comment:
It's true that PHP's behavior doesn't make a lot of sense from a theoretical
perspective. However, there are some practical reasons why a different behavior would be -- arguably
-- less desirable.
Namely, in PHP the constructor can be called from every instance method, even after construction.
This makes it a necessity that the constructor act like regular instance methods. Consider:
<?php
class A {
private $a;
function __construct() { $this->a = new stdclass; }
function reset() { $this->__construct(); }
}
class B extends A {
private function __construct() { } //what of reset() now?
}
Plus, PHP allows enforcing constructor signatures via interfaces. This means you have to enforce
that signature throughout the hierarchy, and this includes not allows changing the visibility of the
constructor.
Similarly, there's no principled reason to be unable to reduce the visibility in static
methods. But PHP also prohibits such a pattern, like Java does, even though there's no
overriding (the method in the superclass is said to be hidden). But PHP, like Java, allows calling
static methods through an instance and through the subclass name. Then if you call the reduced
visibility static method with the subclass name or a subclass instance, what would you do? Would it
depend on the access of the caller has to the subclass method?
Previous Comments:
------------------------------------------------------------------------
[2012-05-07 18:47:00] postmaster at greg0ire dot fr
fixed the title
------------------------------------------------------------------------
[2012-05-07 18:40:56] postmaster at greg0ire dot fr
Description:
------------
Restraining the __construct() method un a subtype gives a Fatal error.
As stated in the following resources, the LSP should not apply here.
- https://bugs.php.net/bug.php?id=40880
- http://stackoverflow.com/questions/5490824/should-constructors-comply-with-the-liskov-substitution-principle
- http://ralphschindler.com/2012/03/09/php-constructor-best-practices-and-the-prototype-pattern
Test script:
---------------
<?php
class Foo {
public function __construct(){}
}
class Bar extends Foo {
protected function __construct(){}
}
Expected result:
----------------
No output at all.
Actual result:
--------------
> PHP Fatal error: Access level to Bar::__construct() must be public (as in class Foo) in
> /tmp/bug.php on line 9
> Fatal error: Access level to Bar::__construct() must be public (as in class Foo) in
> /tmp/bug.php on line 9
------------------------------------------------------------------------
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Edit this bug report at https://bugs.php.net/bug.php?id=61970&edit=1
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