RE: [PHP-DEV] Operator precedence is undefined?

> -----Original Message----- > From: yohgaki@gmail.com [mailto:yohgaki@gmail.com] On Behalf Of > Yasuo Ohgaki > > Hi all, > > 2013/7/21 Sherif Ramadan <theanomaly.is@gmail.com> > > > The problem is I'm not sure where this type of information should > be > > documented. It makes sense to put this on the increment/decrement > operators > > page, but doesn't seem appropriate the operator precedence page. > So to make > > sure we're all in agreement I'm suggesting the following language > to be > > added as a note on the increment/decrement operators page at > > www.php.net/language.operators.increment with supplement examples > > provided above to help users get a better understanding of what we > mean > > when we say undefined behavior and add an additional warning box > not to > > rely on this type of behavior. > > > > Since the issue int "++$a + $a++" is not a precedence issue, but a > evaluation orders and side effects. Describing it without complete > explanation in precedence section makes users confuse. (I'm the one > also) > > I partially agree that documenting the issue in > www.php.net/language.operators.increment . It would better to be > described > fully in a section since it is not a increment/decrement only issue. I agree with this, mostly. It might well be appropriate to document that, as a general rule, there is no guarantee in which order the operands of an arithmetic (at least) operator are evaluated. And you are quite right that it's not only increment/decrement operators, although those are the most obvious culprits. Take the following (very contrived!) example: function f($n) { echo $n; return $n; } $x = f(1) + f(2); For the same reason that the ++$a + $a++ example is undefined, it's undefined whether that will echo 12 or 21 -- even though it's perfectly well defined that $x will be 3 in either case! For this reason, I'd probably go with the major warning being on the precedence/associativity table, with a prominent reference to it on the ++/-- page. Just my £0.02! Cheers! Mike -- Mike Ford, Electronic Information Developer, Libraries and Learning Innovation, 403a Leslie Silver Building, City Campus, Leeds Metropolitan University, Woodhouse Lane, LEEDS,  LS1 3ES,  United Kingdom E: m.ford@leedsmet.ac.uk T: +44 113 812 4730 To view the terms under which this email is distributed, please go to http://disclaimer.leedsmet.ac.uk/email.htm