Re: PHP header files, restrict to declaring code only

On Mon, May 13, 2019, at 7:49 AM, Johannes Schlüter wrote: > On Fr, 2019-05-10 at 15:14 +0200, Lynn wrote: > > Hi Nikita, > > > > By limiting a header file to declaring code only, a couple of issues > > could > > be tackled: > > > > 1. No side effects when loading files. You can assume the global > > state > > remains the same, no > >    code is executed by this file, and no output can be sent. > > Mind that this won't be side-effect free. Declaring a class/function is > a side-effect in itself. > > For dealing with syntax differences we could use the declare() > statement, as used for strict_types or encoding. > > A question is whether it is worthwhile to have multiple syntaxes in > parallel. This adds burden for developers using PHP, (i.e. copying code > from tutorials or other files might fail sometimes etc.) tools > processing PHP (IDEs, code analyzers, ...) and language developers (new > syntax changes have to be evaluated for both contexts) > > If this were a strategy to transition to a new syntax (deprecating "old > PHP") such a mechanism would be the way to go. For just having > alternatives to avoid a syntax conflict cost imo is too big. > > johannes Another possible place such a marker could be useful is in the new preloading functionality in 5.4. Any file that is preloaded is going to never execute again, ever. That means preloading a file that has both symbol declarations and executing global code could lead to weird results. I could see a preloader that would only try to preload symbol-only files. That said... most polyfill files, of which there are a decent number, do some variation on: <?php if (!function_exists('coolness')) { function coolness(int $coolLevel) { ... } } ?> Which would then be incompatible with such a check, yet are perfectly valid to preload; maybe even an especially good case for preloading. So such a strict check is probably unwise. Maybe it would be helpful for the various experimental "precompile PHP" efforts, like what Anthony Ferrara has been doing? I've no idea there. I appreciate the intent here, and agree most code files should be symbol-only, but I'm not sure there's a strong enough use case in practice for it. That said, were it to be adopted I would strongly favor a declare rather than a different file extension or tag. Something like: <?php declare('strict_types=1'); declare('this file only declares symbols, error if it tries to do anything else'); class Blah { ...} ?> That would be the least obtrusive way of adding it, I think. --Larry Garfield