PHP - Interface inheritance - declaration must be compatible

Question

I have the interface:

interface AbstractMapper
{
    public function objectToArray(ActiveRecordBase $object);
}

And classes:

class ActiveRecordBase
{
   ...
}

class Product extends ActiveRecordBase
{
   ...
}

========

But I can't do this:

interface ExactMapper implements AbstractMapper
{
    public function objectToArray(Product $object);
}

or this:

interface ExactMapper extends AbstractMapper
{
    public function objectToArray(Product $object);
}

I've got the error " declaration must be compatible "

So, is there a way to do this in PHP?

Answer 1

No, an interface must be implemented exactly . If you restrict the implementation to a more specific subclass, it's not the same interface/signature. PHP doesn't have generics or similar mechanisms.

You can always manually check in code, of course:

if (!($object instanceof Product)) {
    throw new InvalidArgumentException;
}

Answer 2

Another way of implementing this would be:

class Executor
{
    public function objectToArray(AbstractMapper $var)
    {
        $this->convert($var);
    }

    private function convert(Product $var)
    {
        ...
    }
}