Re: Declaration of Bar::__construct() must be compatible with that of Foo::__construct()
| From: | Marcus Boerger | Date: | Thu, 26 Feb 2004 00:38:08 +0000 |
| Subject: | Re: Declaration of Bar::__construct() must be compatible with that of Foo::__construct() | ||
| References: | 1 2 3 4 | Groups: | php.internals |
| Request: | Send a blank email to internals+get-8135@lists.php.net to get a copy of this message | ||
Hello Timm,
Thursday, February 26, 2004, 12:34:31 AM, you wrote:
> On Wed, 2004-02-25 at 23:52, Timm Friebe wrote:
>> On Wed, 2004-02-25 at 23:44, Marcus Boerger wrote:
>> > Hello Timm,
>> >
>> > i had the same expirience today too. And also for me it makes not much
>> > sense. The constructor shouldn't check inheritance rules.
>>
>> Neither should other methods follow this. What if I want to add a
>> non-default parameter to an overriden method?
> Some test cases:
> Should work #1, Bar::connect() adds an argument
No the sugnature is incompatible. An instance of Foo cannot be called
with Bar or Connector's connect() Signature. Hence Bar is not a Foo
or Connector.
> -------------------------------------------------------------------
> <?php
> interface Connector {
> function connect($server);
> }
> class Foo implements Connector {
> function connect($server) { }
> }
> class Bar extends Foo {
> function connect($server, $port) { }
> }
?>>
> Should work #2, Bar::connect() might contain something such as
Same asas above
> parent::connect('foo.example.com');
> -------------------------------------------------------------------
> <?php
> interface Connector {
> function connect($server);
> }
> class Foo implements Connector {
> function connect($server) { }
> }
> class Bar extends Foo {
> function connect() { }
> }
?>>
> Should work #3, Bar::connect() might contain something such as
Same as above. Foo::connect() can be called with any value
Bar::connect() not.
> parent::connect($dsn->getHost());
> -------------------------------------------------------------------
> <?php
> class DSN { }
> interface Connector {
> function connect($server);
> }
> class Foo implements Connector {
> function connect($server) { }
> }
> class Bar extends Foo {
> function connect(DSN $dsn) { }
> }
?>>
> Should work #4, Foo::connect() adds a default argument
Should work, since the calling convention from Connector is still
possible in Foo and Bar. Hence Foo::connect() IS-A Connector::connect()
and Bar::connect() IS-A Connector::connect().
> -------------------------------------------------------------------
> <?php
> interface Connector {
> function connect($server);
> }
> class Foo implements Connector {
> function connect($server, $port= 42) { }
> }
> class Bar extends Foo {
> function connect($server, $port= 23) { }
> }
?>>
> Should work #5, both interface and implementer have a default value
> for the argument "server"
Should work. Connector's calling convention is till valid in Bar.
Hence Foo::connect() IS-A Connector::connect() and Bar::connect()
IS-A Connector::connect().
> -------------------------------------------------------------------
> <?php
> interface Connector {
> function connect($server= 'localhost');
> }
> class Foo implements Connector {
> function connect($server= 'localhost') { }
> }
> class Bar extends Foo {
> function connect($server= 'localhost', $port= 23) { }
> }
?>>
> Should work #6, implementation adds a default value
Same as #5 only more complicated.
> -------------------------------------------------------------------
> <?php
> interface Connector {
> function connect();
> }
> class Foo implements Connector {
> function connect($server= 'localhost') { }
> }
> class Bar extends Foo {
> function connect($server= 'localhost', $port= 23) { }
> }
?>>
> Should NOT work #1, Foo doesn't fully implement connect()
Right shouldn't work.
> -------------------------------------------------------------------
> <?php
> interface Connector {
> function connect($server);
> }
> class Foo implements Connector {
> function connect() { }
> }
> class Bar extends Foo {
> function connect($server, $port) { }
> }
?>>
> Should NOT work #2, class / primitive clash on argument
Wrong. Should work. Foo::connect() IS-A Connector::connect() and
Bar::connect() IS-A Connector::connect(). It is no problem that a
derived clsses method accepts a greater value range or set of types.
> -------------------------------------------------------------------
> <?php
> class DSN { }
> interface Connector {
> function connect(DSN $dsn);
> }
> class Foo implements Connector {
> function connect($dsn) { }
> }
> class Bar extends Foo {
> function connect($dsn) { }
> }
?>>
> Should NOT work #3, Foo implements Connector::connect() incorrectly
Should work. Still Foo::connect() IS-A Connector::connect()
and Bar::connect() IS-A Connector::connect().
> -------------------------------------------------------------------
> <?php
> interface Connector {
> function connect($server);
> }
> class Foo implements Connector {
> function connect($server, $port) { }
> }
> class Bar extends Foo {
> function connect($server, $port= 23) { }
> }
?>>
> Should NOT work #4, Foo implements Connector::connect() incorrectly
Right, shouldn't work. Inheritance doesn't apply since the signatures
are incompatible.
> -------------------------------------------------------------------
> <?php
> interface Connector {
> function connect();
> }
> class Foo implements Connector {
> function connect($server) { }
> }
> class Bar extends Foo {
> function connect($server, $port) { }
> }
?>>
> I would simply refrain from calling
> zend_do_perform_implementation_check() in inheritance.
> - Timm
--
Best regards,
Marcus mailto:helly@php.net