Re: Re: Straw poll: Places to allow function calls in constant expressions

On Wed, Feb 19, 2020 at 12:58 PM tyson andre <tysonandre775@hotmail.com> wrote: > Hi internals, > > > I've created a straw poll at > https://wiki.php.net/rfc/calls_in_constant_expressions_poll , > to measure > interest in allowing calls in different types of constant expressions. > > If there aren't any problems with the poll structure or rules preventing > creating a poll, I was going to add it to the rfc index page and move it to > voting. > > This straw poll has been moved to voting and added to the rfc index page. > The poll will be closed on March 4th. > The original motivation was, IIRC, to initialize class constants with an expression. Following KISS, I feel we should constrain our efforts to that scope, and that's how I voted: "Yes" on class constants and static members, "No" on everything else. As for implementation, we must manage the complexity. I'm a hard "No" on restricting use to an arbitrary, variable list of blessed functions. It's a dev UX nightmare to include a bevy of array_* functions but no str* functions. 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. <?php class Config { public const URL = null; // compile time initialization protected static $mtime = null; // compile time initialization private static function __constructStatic() { $env = json_decode(file_get_contents('config.json')); self::URL = $env->url; self::$mtime = filemtime('config.json'); } public function reload() { if (self::$mtime < filemtime('config.json')) self::__constructStatic(); } } } echo Config::URL; // assert: runtime has already called _constructStatic $config = new Config; // assert: __constructStatic called only once by runtime $config->reload(); // instance may call its own static constructor ?> 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. Thank you, Tyson, for taking the time to progress this feature. [1]: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/static-constructors