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Date: Tue, 22 Nov 2005 12:48:51 -0800
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To: Matthias Pigulla <mp@webfactory.de>
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Subject: Re: AW: AW: [PHP-DEV] PDM Meeting Notes
From: rasmus@lerdorf.com (Rasmus Lerdorf)

Matthias Pigulla wrote:
> Now that was a quick reply :)
> 
>> Also known as runtime inheritance, or late binding.  It's not a new 
>> thing, we have it today.  The discussion was about whether to 
>> have a way 
> ...
> 
> That is, one can write 
> if (...) class A extends X {} else class A extends Y {} 
> right now? Seriously ;)?
> 
> Every now and then I'm surprised what weird sort of stuff is allowed in
> PHP :), but most probably you don't really want to write this sort of
> code in the first place? ;)

Well, or do a conditional include or an include_once and you end up 
having to do late binding too.  It doesn't have to be as weird as your 
example, but yes, that works too.

>> Just like any other signature in an instance, it tells anything that 
>> implements the interface that it must have a constructor and that 
>> constructor must meet the definition in the interface.  Useful for 
>> object factories.  In most cases you don't want to force a specific 
>> constructor in which case you wouldn't specify it in the 
>> interface, but 
>> I see no reason why you shouldn't be allowed to specify it 
>> there if you 
>> want to.
> 
> The point is that interfaces are nothing you could anything with - that
> is, if you have "something" that implements an interface, it has already
> been constructed. You never construct instances through an interface
> (you would have to choose an implementation, the interface isn't one)...
> I just cannot explain it in a better way ;) It's somewhat similar to
> that you cannot make static calls on interfaces.

I don't see why you can't specify that a class definition must have a 
constructor.  Obviously the constructor is not for the interface itself.

-Rasmus