FUDforum
Fast Uncompromising Discussions. FUDforum will get your users talking.

Home » Imported messages » comp.lang.php » Strange but true! Working with interfaces in PHP
Show: Today's Messages :: Unread Messages :: Polls :: Message Navigator
| Subscribe to topic | Remove from bookmarks 
Return to the default flat view Create a new topic Submit Reply
Strange but true! Working with interfaces in PHP [message #185450] Mon, 31 March 2014 18:31 Go to previous message
Mirco is currently offline  Mirco
Messages: 1
Registered: March 2014
Karma:
Junior Member
add to buddy list
ignore all messages by this user
I was working on a software of arbitrary complexity when I stumbled upon this strange behavior of the PHP compiler.

Problem:
I have these interfaces and classes:

interface IBaseA {

}

interface IA extends IBaseA {

}

interface IBaseB {

public function match( IBaseA $subject );

}

interface IB extends IBaseB{
}

class A implements IA{

}

class B implements IB{
public function match( IA $subject ){
echo "Am I working? o_O<hr>";
}
}

$a = new A();
$b = new B();
$b->match($a);

Running the above code, this is what I get:
Fatal error: Declaration of B::match() must be compatible with that of IBaseB::match()

This behavior is very odd, because A implements IA that extends from IBaseA. So IA is an interface of type IBaseA. Methods I will put in IBaseA will be also in IA.
Class B accepts, in the match() method, an instance of IA.
Class B extends from IBaseB that in turn accepts an instance of IBaseA.

B should accept IA. In fact the interface that B implements accepts a more specific version of IA, but the Fatal Error still pops up.

The things become more strange if we look at another example.
This one:

interface IBaseA {

}

interface IA extends IBaseA {

}

interface IBaseB {

public function match( IA $subject );

}

interface IB extends IBaseB{
}

class A implements IBaseA{

}

class B implements IB{
public function match( IA $subject ){
echo "Am I working? o_O<hr>";
}
}

$a = new A();
$b = new B();
$b->match($a);

Here, what I get it's not a Fatal Error, but a Catchable Fatal Error.
This is an error that could be catched by this simple function:

function myErrorHandler($errno, $errstr, $errfile, $errline) {
if ( E_RECOVERABLE_ERROR===$errno ) {
echo "'catched' catchable fatal error<br>";
return true;
}
return false;
}
set_error_handler('myErrorHandler');

This time though, the compiler should not let me continue with the execution because:

B implements IB that extends from IBaseB.
IBaseB accepts instances of IA.
IA extends from IBaseA.
A implements IBaseA.

What i'm passing to the match() method of B is an instance of A, that is more strict that IA.
The compiler should throw a Fatal Error and it shouldn't let me continue with the execution! The inner details of B's match() implementation require an instance of IA with its own specific methods that could not be provided by IA's father, IBaseA.

Would you please shed a light onto this one?
What do you think about it?
[Message index]
 
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Previous Topic: Need help accessing the key array.
Next Topic: MYSQL PHP Query Not Working
Goto Forum:
  

-=] Back to Top [=-
[ Syndicate this forum (XML) ] [ RSS ]

Current Time: Sat May 18 21:30:13 EDT 2024

Total time taken to generate the page: 0.04802 seconds