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Subject: Re: [PHP-DEV] static constructor
From: rowan.collins@gmail.com (Rowan Collins)

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Patrick Schaaf wrote on 12/03/2015 18:40:
>
> Am 12.03.2015 18:56 schrieb "Rowan Collins" <rowan.collins@gmail.com 
> <mailto:rowan.collins@gmail.com>>:
> >
> > Johannes Ott wrote on 12/03/2015 17:05:
> >
> >>>> So doing a null check each time
> >>>> is a overhead of calculation which can be avoided with this static
> >>>> constructor pattern.
> >>>
> >>> Presumably the engine would need to perform some implicit 
> equivalent of
> >>> "if ( ! self::$initialised )" on each call to decide if the static
> >>> constructor needs to be called or not, so the overhead is not 
> completely
> >>> eliminated.
> >>>
> >> Yes you are right but I think it can be done more efficiently 
> inside the
> >> interpreter using some struct flags then have to parse each time inside
> >> a coded part in the application.
> >
> > Yes, point taken.
>
> I don't think such a flag is neccessary at all. Any class. at the 
> moment, comes from one or another file that is included / required. 
> And all of the code in these files outside the class definition, is 
> then immediately executed. The only thing neccessary would be to 
> check, just before that execution begins, which of the new classes 
> have such an initializer method, and then call that, before the 
> execution of the file itself begins.
>

This was my initial interpretation, but Johannes has explained that that 
is not the intention of this proposal. Instead, it is intended to be 
called on first *use* of the class; a subtle difference, but given this 
code:

class A { public static $foo; private function __static() { echo 'A'; } }
class B { public static $foo; private function __static() { echo 'B'; } }
B::$foo = 1;
A::$foo = 2;

Running the magic at definition time will echo 'A' then 'B'; running it 
on first use will echo 'B' then 'A'.


> Incidentally that is something that cannot be emulated with the 
> autoloader-does-it approach, because the autoloader can only do that 
> after the include/require is complete - i.e. code within the file will 
> not yet see the class as initialized (in that approach).

For that scenario, the autoloader can immediately call 
$class_name::__static() or whatever. The only edge-case is when you try 
to also put loose code in your class definition files, but why would you 
need to?

Regards,
-- 
Rowan Collins
[IMSoP]

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