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

> 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. I'd also personally found the static $x = null; if ($x === null) { $x = some_fn(); } pattern inconvenient and wanted that to be just static $x = some_fn(); to make the initial value some_fn() if possible. It also seemed more readable (e.g. doesn't matter if some_fn() can be constant). My personal use case for parameter defaults and global constants isn't as strong (especially with define()), but it's still something I'd want. - I'd be able to use private const FOO_DEFAULT = array_keys(...); function foo($x = FOO_DEFAULT) {} if constants did pass, so that's less off a concern, and ensures&makes clear that the expression is only evaluated once, so it might be a better place to start with. > 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. If the RFC succeeded with a whitelist, I'd planned to create RFCs to add to the whitelist. Locale dependency of string functions was the reason for leaving it out initially, since that may also be a hard "no" for others. > 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 > $config->reload(); // instance may call its own static constructor ?> This seems to allow the same functionality my RFC would allow, in a slightly different way. I didn't go with that syntax because it'd move the values of the constants/properties away from the declaration. Also, if json_decode() threw, then there would never be a way for a PHP implementation to initialize self::$mtime in that example, even though they're unrelated in how they're initialized there. Allowing calling __constructStatic multiple times (thus assigning to the **const** self::URL multiple times) would be a significant change to php internals, and out of the scope of this RFC https://wiki.php.net/rfc/calls_in_constant_expressions_poll ("Put the RFC(Poll) URL into all your replies.") - Tyson