Edit report at https://bugs.php.net/bug.php?id=40880&edit=1
ID: 40880
Comment by: postmaster at greg0ire dot fr
Reported by: prometheus__0 at hotmail dot com
Summary: public->protected inheritance causes fatal
Status: Not a bug
Type: Bug
Package: Class/Object related
Operating System: SUSE SLES 10
PHP Version: 5CVS-2007-03-21 (snap)
Block user comment: N
Private report: N
New Comment:
@rasmus:
Then why is there a strict warning regarding the compatibility of method
signatures for this code:
--------------
class Foo {
public function test() {
}
}
class Bar extends Foo {
public function test(ArrayObject $arrayObj, $number = 0) {
/* do stuff with $arrayObj and $number */
}
}
---------------
and not for this one:
---------------
class Foo {
public function __construct() {
}
}
class Bar extends Foo {
public function __construct(ArrayObject $arrayObj, $number = 0) {
/* do stuff with $arrayObj and $number */
}
}
------------
No, as stated here :
-
http://stackoverflow.com/questions/5490824/should-constructors-comply-with-the-liskov-substitution-principle
- and here:
http://ralphschindler.com/2012/03/09/php-constructor-best-practices-and-the-prototype-pattern,
the LSP does not apply to constructors for several reasons:
- When you call the constructor, you know whether you're using the type or one
of its subtypes.
- You can't apply the LSP to an object that does not exist yet.
I think this is a design flaw. Not "massive", but a design flaw indeed.
Previous Comments:
------------------------------------------------------------------------
[2012-05-06 16:12:00] ras...@php.net
Most (all?) object oriented languages work this way. Java and C# both do. You
can
loosen visibility when you override a parent method, but you can never tighten
it. This is part of what is known as the Liskov Substitution Principle and it
is
one of the fundamental principles of object oriented programming. You can read
about at http://en.wikipedia.org/wiki/Liskov_substitution_principle
I can guarantee that abiding by LSP is not a bug
------------------------------------------------------------------------
[2012-05-06 15:40:26] ekincigokan at gmail dot com
Same "problem".
class A{
public function __construct(){}
}
class B extends A {
protected function __construct(){}
}
Please, can you tell us a reason why we can't put an private/protected access
to B's constructor if A's constructor is public ?
Is there any logical reason to this ?
Thanks.
------------------------------------------------------------------------
[2011-09-10 22:27:24] herman dot wetherington at gmail dot com
Apparently, we don't call this a "bug" because this is not caused by a
programming error. So I'm calling it a "massive design flaw" instead.
------------------------------------------------------------------------
[2010-10-15 23:33:35] robertoblanko at gmail dot com
Same problem here. You cannot actually apply the singleton pattern to
subclasses with this behavior. I do not see any reason for not calling this a
bug.
------------------------------------------------------------------------
[2010-09-07 12:58:35] nickyla83 at yahoo dot fr
I'm in the same situation as our friend "prometheus" here, I am trying to use a
singleton pattern and logically, this should involve being able to encapsulate
the subcalasses information particularly setting up a private constructor for
the singleton subclass, IT DEFINITELY DOES MAKE SENSE, so please try to take
this under consideration for the next php engine release.
------------------------------------------------------------------------
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