Inheritance/compatibility behavior

I want to make two classes:

abstract class a {
abstract public function go($a);
}
final class b extends a {
abstract public function go(array $a);
}

Sorry, function in class b should not be abstract.

This will not work, I get an error that the two must be compatible.
Wouldn't it be a good idea to allow any type hint for a parameter that
does not specify a type hint?

Ie, I can do the above, but not the following:

abstract class a {
abstract public function go(myClass $a);
}
final class b extends a {
abstract public function go(array $a);
}

Same, function in class b should not be abstract.

On Tuesday 29 April 2008 15:34:07 Sam Barrow wrote:

This will not work, I get an error that the two must be compatible.
Wouldn't it be a good idea to allow any type hint for a parameter that
does not specify a type hint?

That would be a bad idea, because it violates a (in my opinion, the) core
principle of OO: If B inherits from A, anything I can do with A (i.e. pass an
int to the method go) I can do with B.
http://en.wikipedia.org/wiki/Liskov_substitution_principle

Regards,
Stefan

P.S. Sorry if this pops up twice, used the wrong from: address at first ...

Hi!

Sam Barrow wrote:

I want to make two classes:

abstract class a {
abstract public function go($a);
}
final class b extends a {
abstract public function go(array $a);
}

LSP violation here: a accepts go("away") but b doesn't.

This will not work, I get an error that the two must be compatible.
Wouldn't it be a good idea to allow any type hint for a parameter that
does not specify a type hint?

No, because of the LSP. Subtypes should not strengthen preconditions.

Stanislav Malyshev, Zend Software Architect
stas@zend.com http://www.zend.com/
(408)253-8829 MSN: stas@zend.com