Re: [PHP] Execution order of PHP

On Wed, 2010-03-10 at 15:20 +0100, Sándor Tamás wrote:

> 
> 2010.03.10. 14:41 keltezéssel, Bob McConnell írta:
> > From: Auke van Slooten
> >
> >    
> >> In a hobby project I'm relying on the order in which the following
> >>      
> > piece
> >    
> >> of PHP code is executed:
> >>
> >> $client->system->multiCall(
> >>     $client->methodOne(),
> >>     $client->methodTwo()
> >> );
> >>
> >> Currently PHP always resolves $client->system (and executes the __get
> >>      
> > on
> >    
> >> $client) before resolving the arguments to the multiCall() method
> >>      
> > call.
> >    
> >> Is this order something that is specified by PHP and so can be relied
> >> upon to stay the same in the future or is it just how it currently
> >>      
> > works.
> >    
> >> If it cannot be relied upon to stay this way, I will have to rewrite
> >>      
> > the
> >    
> >> multiCall method and API...
> >>      
> > Think about it from the parser's point of view. It has to evaluate
> > $client->system to determine the parameter list for multiCall(). Then it
> > has to evaluate those parameters before it can stuff their values into
> > the stack so it can call the function. But, whether it evaluates the
> > parameter list left-to-right or vice versa is implementation dependent.
> > I don't believe you can rely on it always being the same unless you
> > always use the same interpreter.
> >
> > Bob McConnell
> >
> >    
> I think it cannot be that the evaluation order of the parameters is 
> implementation dependent.
> Just think about it:
>    $someobject->method($a++, $a++);
> 
> What will be the result? Or there has to be some directive to tell the 
> parser to evaluate the parameters from left to right or vice versa.
> And if there isn't, in some future release, there has to be.
> 
> SanTa
> 


The order is implementation dependent, and just follows from other
languages which behave exactly the same (I believe Java and C++ both do)

This is the sort of example that's used as a reason to not rely on such
behaviour. You just have to work around it I guess.

Thanks,
Ash
http://www.ashleysheridan.co.uk