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Date: Tue, 12 May 2009 15:29:07 +0400
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Subject: Re: [PHP-DEV] Method call improvements
From: dmitry@zend.com (Dmitry Stogov)



Paul Biggar wrote:
> On Tue, May 12, 2009 at 9:43 AM, Dmitry Stogov <dmitry@zend.com> wrote:
>>> Apologies, I'm not familiar with run-time inheritence in PHP. My
>>> understanding was that when a classes source code is compiled, its
>>> parent classes must be known. When is this not the case?
>> The parent class may be defined in other file that is loaded at runtime
>> using include() statement. It's very usual case. So the PHP first loads the
>> include file and then declares child class at runtime.
> 
>>> Must it be known for the class' first instantiation?
>> Of course. :)
> 
> 
> On Tue, May 12, 2009 at 7:25 AM, Dmitry Stogov <dmitry@zend.com> wrote:
>> The real things is even worse as during compilation of a class it's parent
>> class doesn't have to be known. So construction of VMTs becomes a bit
>> problematic. BTW we could think in this way...
> 
> 
> OK, so I dont understand this exactly. Is it correct to say that if a
> class uses inheritance its compilation will be deferred until its
> first instantiation? Or is it compiled when it is seen, and its parent
> backpatched in later. When is later?

The classes which parent isn't known during compilation inherited at 
run-time by DECLARE_INHERITED_CLASS opcode. It patches property and 
method tablas, checks for method compatibility, etc

> But I think its fair to say that it has static inheritance - that is,
> its full inheritance chain is known before it can be instantiated, and
> it can never be changed after that.

Right, but it has a lot of dynamic issues anyway. E.g. parent class may 
be changed or loaded from different file.


Thanks. Dmitry.

> 
> 
> 
> 
>>> In the worst case, it _might_ be cheaper to build it at instantiation
>>> time, but I would have to look up how expensive that is in a more
>>> static language to be sure. Certainly, it is currently so expensive
>>> that almost anything else would be better (including the OP's patch).
>> I don't see how run-time VMT contraction may help, because calls to virtual
>> method must know VMT offset at compile-time.
> 
> Right. Construction is fine. Their use is not. I don't know what I was
> thinking.
> 
> 
> 
> So it looks like the best way forwards is still the OP's patch?
> 
> 
> 
> Thanks,
> Paul
> 
> 
>