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Thread-Topic: [RFC] Allow calls to global functions in constant expressions
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Date: Sun, 9 Feb 2020 21:02:39 +0000
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Subject: [RFC] Allow calls to global functions in constant expressions
From: tysonandre775@hotmail.com (tyson andre)

Hi internals,=0A=
=0A=
https://wiki.php.net/rfc/calls_in_constant_expressions has been updated and=
 moved to=0A=
"Under Discussion".=0A=
=0A=
This proposes allowing function calls in constant declarations, static prop=
erty defaults,=0A=
static variables, and parameter defaults.=0A=
It includes a secondary voting option to allow any function calls,=0A=
and not just a small set of whitelisted core functions.=0A=
Other expression types would continue to be forbidden in constant expressio=
ns (variables, method calls, etc)=0A=
=0A=
Let me know if you have any comments on the RFC or implementation.=0A=
=0A=
Earlier discussion can be found in https://externals.io/message/108343=0A=
("Planning an RFC to allow calls to global functions in constant expression=
s")=0A=
=0A=
I made some updates to the RFC, implementation and the proposed whitelist o=
f functions.=0A=
(in response to https://externals.io/message/108343#108427)=0A=
=0A=
> > As you've already realized, the main problem here is the behavior for=
=0A=
> > functions that have side-effects or state. Currently we mostly get away=
=0A=
> > with the illusion that it doesn't matter when exactly constexpr=0A=
> > initializers are evaluated. Apart from the error location and (admitted=
ly=0A=
> > quite a few) other details, you ostensibly can't distinguish whether th=
e=0A=
> > expression is going to evaluated on declaration, on first access or on =
each=0A=
> > access.=0A=
>=0A=
> Good point - If PHP ends up supporting an option where **any** global fun=
ction can get called,=0A=
> It'd make sense to evaluate any expression *with a function call*=0A=
> every time for instance properties and parameter defaults=0A=
> (e.g. `public $id =3D generate_unique_int_id()`).=0A=
> (the optimizer can later optimize any functions where it won't be noticea=
ble).=0A=
>=0A=
> I think that would require updates to my PR for caching,=0A=
> since immutable returned zvals (including false/true) get cached permanen=
tly.=0A=
=0A=
I've completed the updates to parameter defaults.=0A=
Parameter defaults containing calls now don't get cached:=0A=
They always get evaluated every time the parameter isn't passed in.=0A=
=0A=
I also excluded support for calls in instance property defaults from the RF=
C.=0A=
I'd want that feature, but the changes to PHP's internal representation of =
classes expand=0A=
the scope of this RFC too much for me.=0A=
=0A=
- PHP currently evaluates all the property defaults and permanently caches =
them=0A=
  the first time a property gets accessed or an object gets instantiated.=
=0A=
  I'd probably have to change the internal class representation as well to =
fix that,=0A=
  and I don't know how many or what types of bugs/issues that would cause.=
=0A=
=0A=
> That reminds me:=0A=
> I forgot about functions such as `compact()`, `extract()` and `get_define=
d_vars()`.=0A=
> (and `func_num_args()`/`func_get_args()`/`func_get_arg()`).=0A=
> It looks like all of them check `zend_forbid_dynamic_call()` to throw,=0A=
> but I need to add tests and possibly flag the call as dynamic.=0A=
=0A=
Update: The implementation already properly throws an Error.=0A=
=0A=
Thanks,=0A=
- Tyson=