Re: [RFC] [VOTE] Constant scalar expressions

Hi all, On Fri, Nov 22, 2013 at 10:19 AM, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote: > On Fri, Nov 22, 2013 at 10:09 AM, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote: > >> Anyway, constant variables are useful for VM/op code optimization. >> >> include('foo.php'); // const a = 123; >> const b = a; >> >> is allowed currently. We may restrict this behavior only to the same file, >> so that VM/op code optimization can be done. >> >> Currently, no expression is allowed with 'const'. Defining 'const' >> using >> another constant with the same value is useless. It's a bad coding >> practice >> in many case, I suppose. >> >> I understand use cases of scalar expressions with constants, but I'm >> concerned >> loosing door for further optimizations. (e.g. $x = $x + 123 is faster >> than $x = $x + a, >> where a is 123 in constant var hash) >> >> We may be better to restrict expressions with constants only to the same >> file >> even if we loose some benefits/flexibility in user code. >> >> Is this discussed? >> > > I voted 'yes', but I change my mind. Sorry. > If the RFC leaves door for constant optimization, I'll vote 'yes'. > Constant look up is not a simple hash look up. > One more additional note why I decided to vote 'no' for this. We already have dynamic constant via define(). <?php define('A', 123); define('B', A*2); echo B; // 246 ?> We can even use function return values with define(). <?php function foo() { return 123; } define('A', foo()); echo A; // 123 ?> I prefer 'const' to be a static for better performance, since we have dynamic constant by define() already. Regards, -- Yasuo Ohgaki yohgaki@ohgaki.net