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Date: Wed, 19 Feb 2020 14:21:46 -0500
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To: bishop@php.net
Subject: Re: [PHP-DEV] Re: Straw poll: Places to allow function calls in
 constant expressions
From: mike@newclarity.net (Mike Schinkel)



> On Feb 19, 2020, at 2:00 PM, Bishop Bettini <bishop@php.net> wrote:
>=20
> Consequently, the only way to safely initialize class constants and =
static
> members is at run-time, and I can only think of one way to do it. =
Apologies
> if this has already been suggested: taking a cue from C#, a static =
class
> constructor ([1]) would allow us to have expression-initialized =
constants
> and static members.
>=20
> <?php
> class Config {
>    public const URL =3D null; // compile time initialization
>    protected static $mtime =3D null; // compile time initialization
>    private static function __constructStatic() {
>        $env =3D json_decode(file_get_contents('config.json'));
>        self::URL =3D $env->url;
>        self::$mtime =3D filemtime('config.json');
>   }
>   public function reload() {
>       if (self::$mtime < filemtime('config.json'))
>           self::__constructStatic();
>       }
>   }
> }
>=20
> echo Config::URL; // assert: runtime has already called =
_constructStatic
> $config =3D new Config; // assert: __constructStatic called only once =
by
> runtime
> $config->reload(); // instance may call its own static constructor
> ?>
>=20
> Trying to do the same for global constants, static variables, or =
function
> default parameters resists a similar initialization mechanism because =
we
> don't have defined common entry point analogues. If we had a main(), =
or if
> we had framed @before decorators, we could do something similar, but =
we
> don't -- so I feel we should leave these off the table.

For different reasons than this RFC I have wanted a static class =
constructor for a really long time.=20

I hope this is something we can seriously consider.   Thanks Bishop for =
proposing it.

-Mike=