Edit report at https://bugs.php.net/bug.php?id=46705&edit=1
ID: 46705
Comment by: clicky at erebot dot net
Reported by: wrzasq at gmail dot com
Summary: Impossible to implement compatible interfaces
Status: Open
Type: Feature/Change Request
Package: Scripting Engine problem
Operating System: Debian GNU/Linux
PHP Version: 5.2.6
Block user comment: N
Private report: N
New Comment:
tklingenberg at lastflood dot net:
I think you missed the point, or to rephrase it another way: the problem lies
in the definition of "compatible":
<?php
interface A
{
public function foo();
}
interface B
{
public function foo();
}
class C implements A, B
{
public function foo(){}
}
?>
and
<?php
interface A
{
public function foo();
}
interface A
{
public function foo();
}
class C implements B
{
public function foo(){}
}
?>
should both be considered valid scripts because the two signatures for foo()
[in interface A and interface B] do not contradict each other: it is possible
to write a method that satisfies both.
The same argument also holds for the example smith gave:
<?php
interface fooI
{
function ding();
}
interface barI extends fooI
{
function ding($dong = null);
}
class bar implements barI
{
public function ding($dong = null)
{
echo 'woho: '.$dong."\n";
}
}
Note however that in this case, it would be invalid if bar implemented both
fooI and barI because the two interfaces contradict each other (one expects an
[optional] argument, while the other doesn't).
Of course your example (already) works because you simply defined an empty
interface (which is rather pointless, unless you're actually extending from
several interfaces).
Maybe another analogy will help. Let's suppose I define 2 interfaces, one for
people, the other one for robots:
<?php
interface Person
{
public function speak();
public function walk();
}
interface Robot
{
public function speak();
public function roll();
}
?>
Now, imagine that I want to create a Humanoid class (a mix between a Person and
a Robot). Quite naturally, I'd want to write something like this:
<?php
class Humanoid
implements Person, Robot
{
public function speak() { echo "Hello world!"; }
protected function goForward($speed) { /* ... */ }
public function walk() { $this->goForward(1); }
public function roll() { $this->goForward(3); }
// some other methods...
}
?>
Unfortunately, this will give you an error such as this:
"PHP Fatal error: Can't inherit abstract function Robot::speak() (previously
declared abstract in Person) in Command line code on line 1"
... and that's what this bug is all about...
It's a PITA when you must work with interfaces defined by other people which
are compatible (ex: both force you to define a "__toString" method) and yet PHP
returns a fatal error when you try to use them in your own class.
Previous Comments:
------------------------------------------------------------------------
[2011-11-27 18:03:02] tklingenberg at lastflood dot net
Actually it's possible, you just need to make the interfaces compatible for
that:
interface A
{
public function foo();
}
interface B extends A
{
}
and then you're done. This also prevents you from writing duplicate code ;)
However if interfaces definitions can not be changed, then this is not a
solution. Probably this is fixed? - See bug #43200.
------------------------------------------------------------------------
[2011-08-01 12:11:11] smith at pooteeweet dot org
Note its also not possible to redefine while adding new optional parameters
<?php
interface fooI
{
function ding();
}
interface barI extends fooI
{
function ding($dong = null);
}
class bar implements barI
{
public function ding($dong = null)
{
echo 'woho: '.$dong."\n";
}
}
$bar = new bar;
$bar->ding('yeah!');
------------------------------------------------------------------------
[2011-03-22 23:33:03] clicky at erebot dot net
I think this use case, the one bug #43200 and the one below are all valid:
<?php
interface A
{
public function foo();
}
interface B
extends A
{
public function foo();
}
class C implements B
{
public function foo(){}
}
?>
The case above may seem odd (there's really no point in redefining the exact
same interface), but I have a simple use case where this may prove handy.
I'm currently writing some code for a little project which is meant to teach
some middle to advanced topics of PHP. The code is self-documented (using
doxygen) and uses some interface from SPL (Countable). That interface is used
several times in different files and I'd like to document the count() method
only once (if possible, at the interface level -- then using doxygen's ability
to copy/paste the doc from parent classes/interfaces into the current class).
I thought I could just define my own interface (Project_Countable), extending
from SPL's Countable, "overriding" the method's signature (only so doxygen can
pick up the method's declaration -- the prototype for the method was actually
left unchanged) and then define a class that implements Project_Countable.
So in my case, A = SPL's Countable interface and B = Project_Countable.
However, this pattern can't be used as it results in the same error others
noted here and in bug #43200.
I can't simply avoid Project_Countable extending from Countable, because then I
would lose count()'s "magic" by doing so.
------------------------------------------------------------------------
[2008-11-28 07:57:42] wrzasq at gmail dot com
Description:
------------
It is impossible to implement multiple interfaces that declares same
methods. I saw bug #43200 but this is a bit different case and I
think in this situation it shoud be allowed - those interfaces
requires methods with same signature (also to prevent further
problems - optional parameters should also be allowed to match
signatures):
Reproduce code:
---------------
<?php
interface A
{
public function foo();
}
interface B
{
public function foo();
}
class C implements A, B
{
public function foo(){}
}
Expected result:
----------------
nothing, but working
Actual result:
--------------
Fatal error: Can't inherit abstract function B::foo() (previously
declared abstract in A) in /home/wrzasq/Desktop/Www/engine/- on line
16
------------------------------------------------------------------------
--
Edit this bug report at https://bugs.php.net/bug.php?id=46705&edit=1
