Edit report at https://bugs.php.net/bug.php?id=62814&edit=1
ID: 62814
Updated by: ni...@php.net
Reported by: resha dot ru at gmail dot com
Summary: It is possible to stiffen child class members
visibility
-Status: Not a bug
+Status: Open
Type: Bug
Package: Class/Object related
Operating System: Linux
PHP Version: 5.3.15
Block user comment: N
Private report: N
New Comment:
I agree with kev here. LSP applies at all hierarchy levels. If the parent is
protected, you can't go private.
C is a subtype of B, but you couldn't use it interchangeably due to different
visibility. So LSP is clearly broken here.
Previous Comments:
------------------------------------------------------------------------
[2012-08-24 18:54:17] kev dot simpson at gmail dot com
You guys have me a bit confused now. You seem to be in agreement that an
inherited method cannot decay the scope of the parent's method (since PHP
doesn't bubble up), yet you are indicating that this isn't a bug.
I'm still curious on how to get around the interfacing issue. For an example:
Test Script:
---------------
<?php
interface IInterface
{
public function test();
}
class Grandfather
{
private function test()
{
return __METHOD__;
}
}
class Father extends Grandfather implements IInterface
{
public function test()
{
return __METHOD__;
}
}
class Son extends Father
{
protected function test()
{
return __METHOD__;
}
}
function printTest(IInterface $i)
{
return $i->test();
}
$aObjs = array(new Father(), new Son());
$rcInterface = new ReflectionClass('IInterface');
foreach ($aObjs AS $obj)
{
$rc = new ReflectionClass($obj);
$testMethod = $rc->getMethod('test');
printf('%s' . PHP_EOL,
str_pad($rc->getName() . ' START', 25, '-', STR_PAD_BOTH));
// Procedural checks
printf('%s instanceof IInterface? %d' . PHP_EOL,
$rc->getName(),
($obj instanceof IInterface));
printf('is_a(%s, IInterface)? %d' . PHP_EOL,
$rc->getName(),
is_a($obj, 'IInterface'));
printf('is_subclass_of(%s, IInterface)? %d' . PHP_EOL,
$rc->getName(),
is_subclass_of($obj, 'IInterface'));
// reflection checks.
printf('(Reflection)%s::implementsInterface(IInterface)? %d' . PHP_EOL,
$rc->getName(),
$rc->implementsInterface('IInterface'));
printf('(Reflection)%s::getInterfaceNames(): %s' . PHP_EOL,
$rc->getName(),
implode(', ', $rc->getInterfaceNames()));
printf('%s::isInstance(%s)? %d' . PHP_EOL,
$rcInterface->getName(),
$rc->getName(),
$rcInterface->isInstance($obj));
print('Methods:' . PHP_EOL);
foreach ($rc->getMethods() AS $method)
{
$objMethod = $rc->getMethod($method->getName());
try
{
$prototype =
$method->getPrototype()->getDeclaringClass();
}
catch (ReflectionException $ex)
{
$prototype = $method->getDeclaringClass();
}
printf("\t%s prototyped by %s is public? %d" . PHP_EOL,
$method->getName(),
$prototype->getName(),
$objMethod->isPublic());
}
printf('Call %s::test() via printTest: %s' . PHP_EOL,
$rc->getName(),
printTest($obj));
printf('%s' . PHP_EOL,
str_pad($rc->getName() . ' END', 25, '-', STR_PAD_BOTH));
print(PHP_EOL);
}
?>
Expected Results:
------------------
Fatal error: Access level to Son::test() must be public (as in class Father)
Actual Results:
------------------
------Father START-------
Father instanceof IInterface? 1
is_a(Father, IInterface)? 1
is_subclass_of(Father, IInterface)? 1
(Reflection)Father::implementsInterface(IInterface)? 1
(Reflection)Father::getInterfaceNames(): IInterface
IInterface::isInstance(Father)? 1
Methods:
test prototyped by IInterface is public? 1
Call Father::test() via printTest: Father::test
-------Father END--------
--------Son START--------
Son instanceof IInterface? 1
is_a(Son, IInterface)? 1
is_subclass_of(Son, IInterface)? 1
(Reflection)Son::implementsInterface(IInterface)? 1
(Reflection)Son::getInterfaceNames(): IInterface
IInterface::isInstance(Son)? 1
Methods:
test prototyped by IInterface is public? 0
Fatal error: Call to protected method Son::test() from context ''
So everything here does indicate that Son is a typeof IInterface, yet it
clearly shows that the prototyped IInterface::test() has been demoted to a
non-public scope.
The only way I can "fix" this is by double checking any check against the
object in question:
function printTest(IInterface $i)
{
$sResult = '';
$rc = new ReflectionClass($i);
$method = $rc->getMethod('test');
if ($method->isPublic())
{
$sResult = $method->invoke();
}
return $sResult;
}
Which given the pass for the IInterface check on the typehint should contract
that object to guarantee the IInterface::test method, yet here we must double
check that its within an accessible scope and therefore violates the interface
contract.
So I need to ask again, what is the purpose of the interface if the class isn't
obligated to implement all the methods in a public scope?
------------------------------------------------------------------------
[2012-08-24 00:35:14] ras...@php.net
Johannes, I think you are actually agreeing with him here. As per Liskov you
can't tighten visibility, you can only loosen it on inheritance. However, in
this
case you aren't tightening it because the original was private, so setting it
back to private is allowed and doesn't violate Liskov.
------------------------------------------------------------------------
[2012-08-23 21:28:49] johan...@php.net
If you'd stiffen visibility you'd be violating the is-a contract given. If an
object is using a classed derived from A and I can do "instanceof A" I expect
to be able to call all methods from A and having them do something like A's
method does. When stiffening that won't be the case anymore.
------------------------------------------------------------------------
[2012-08-23 19:49:18] kev dot simpson at gmail dot com
I reported this same problem a few years ago here:
https://bugs.php.net/bug.php?id=48376
I was told this was not a bug (although I haven't a clue as to why its not
deemed as such). I believe C# allows you the ability to do this as it would
resolve up the scope, but as of 5.4.0 I still cannot get why it allows forced
reduced scopes during declaration, but provides an uncatchable fatal error on
call.
I'm still most concerned by the allowed reduction from an interface. There is
no way to guarantee that an interface will implement the method in question
regardless of if it is known to be that type which truly is a shame.
------------------------------------------------------------------------
[2012-08-14 09:50:47] resha dot ru at gmail dot com
Sorry, it should be:
class F extends D
{
private function test() { } // stiffen visibility from public to private
(unexpected)
}
But nevertheless.
------------------------------------------------------------------------
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the rest of the comments, please view the bug report online at
https://bugs.php.net/bug.php?id=62814
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