PHP does not implement inheritance checks for typehinted arguments. Please also refer to the PDM meeting notes, where this was discussed: http://www.php.net/~derick/meeting-notes.html#implement-inheritance-rules-for-type-hints

Hmm, too bad.

The link you provided about the PDM meeting says "that most probably no language currently implements this correctly" is not true. 

Java for instance does this just nicely at least since 1.3.

With that limitation, the implementation of an AbstractDAO/AbstractFactory pattern will fail if type hinting is wanted, because transfer objects need to be identifyable by their common interface. Otherwise the entire interface thing in PHP does not make much sense, IMHO.

So anyhow, at least the error message should be changed to be more clear.

Hi Derek,

    Thank you for your responses; I ran into this same issue.  I hate to 
resurrect old tickets, but are you sure you want to leave this out?  

    Here is my concern...  There is no point to have type hinting if object 
inheritance is not respected.  For example, let's say I have the following 
interface...

interface Comparable
{
    public function gte(Comparable $value);
    public function lte(Comparable $value);
    public function eq(Comparable $value);
    public function gt(Comparable $value);
    public function lt(Comparable $value);
}

and now I have the following base classes...

class Orange implements Comparable
{
    ...
    public function gte(Comparable $orange) { ... }
    public function lte(Comparable $orange) { ... }
    public function eq(Comparable $orange) { ... }
    public function gt(Comparable $orange) { ... }
    public function lt(Comparable $orange) { ... }
}

class Apple implements Comparable
{
    ...
    public function gte(Comparable $apple) { ... }
    public function lte(Comparable $apple) { ... }
    public function eq(Comparable $apple) { ... }
    public function gt(Comparable $apple) { ... }
    public function lt(Comparable $apple) { ... }
}

Does it REALLY make sense to compare Apples to Oranges???


Kind regards,

John

Derick,

  I'm sorry I misspelled your name.

Sincerely,

John S

Here's an example that shows, why this is not allowed:

<?php
class AnotherBar implements IBar
{
    function getMessage() { }
}

function moo(Foo $foo)
{
    $bar = new AnotherBar();
    $foo->saySomethingElse($bar);
}

moo(new BarDAO());

This would be a syntactically valid code, but it would fail, because BarDAO::saySomethingElse() does not allow AnotherBar.

It is complicated, but it is easier to understand, if you see an example.