Doc #81511 [Nab]: Evaluation order for . operator should be specified

Edit report at https://bugs.php.net/bug.php?id=81511&edit=1 ID: 81511 Updated by: requinix@php.net Reported by: dean at omnivisiontechnology dot com Summary: Evaluation order for . operator should be specified Status: Not a bug Type: Documentation Problem Package: Unknown/Other Function Operating System: n/a PHP Version: Irrelevant Block user comment: N Private report: N New Comment: if ($a) { $s = "option A"; } else if ($b) { $s = "option B"; } else if ($c) { $s = "option C"; } else { $v = expensiveFunction(); $s = "Value is: {$v} other stringy stuff {$v}"; } Previous Comments: ------------------------------------------------------------------------ [2021-10-07 10:25:23] dean at omnivisiontechnology dot com If evaluation order might change, then there's nothing to be done. But I'd note that "clever" or not, this idiom can be very useful in writing concise code, for example buried deep inside nested ternaries, where you can only put an expression and not a statement block, e.g. $s = ($a ? "option A" : ($b ? "Option B" : ($c ? "Option C" : 'Value is: '.($v = expensiveFunction())." other stringy stuff ".$v))); vs if (!($a||$b||$c)) $v = expensiveFunction(); $s = ($a ? "option A" : ($b ? "Option B" : ($c ? "Option C" : 'Value is: '.$v." other stringy stuff ".$v))); which apart from being longer, also contains the same condition check in two places (and in two different formats), leading to potential bugs if one is changed and the other is not. ------------------------------------------------------------------------ [2021-10-07 08:26:41] requinix@php.net It isn't specified because it isn't guaranteed. It's generally left to right, sure, but the exact behavior may change in the future if PHP alters how it parses and executes code. Not guaranteeing behavior also potentially allows caching or optimization extensions more freedom in the benefits they can offer. It's a bad idiom. Don't use it. "Clever" code doesn't benefit anyone. ------------------------------------------------------------------------ [2021-10-07 06:56:50] dean at omnivisiontechnology dot com Description: ------------ --- From manual page: https://php.net/language.operators.string --- In general, PHP doesn't specify the order of evaluation for operators. However, order of evaluation for the string concatenation operator specifically, does always seem to be left then right. If this can indeed be guaranteed, then it should be specified in the documentation, because it enables the very common coding idiom: $string = 'something'.($complicatedSubstring = 'something else').'more stuff'.$complicatedSubstring; Test script: --------------- $s = '[Very bad!]' $x = 'bar '.($s = 'foo').' bar bar '.$s.' bar'; Expected result: ---------------- $x should be 'bar foo bar bar foo bar'. It'd be very unexpected for it to be 'bar foo bar bar [Very bad!] bar', But that's what could happen if the . operator evaluated the RHS first... which fortunately it doesn't appear to. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=81511&edit=1