Bug #78829 [Fbk]: æ°åä¼ å¼ç¨è®¡ç®é®é¢
Edit report at https://bugs.php.net/bug.php?id=78829&edit=1
ID: 78829
Updated by: requinix@php.net
Reported by: 1003674174 at qq dot com
Summary: æ°åä¼ å¼ç¨è®¡ç®é®é¢
Status: Feedback
Type: Bug
Package: Variables related
Operating System: windows
PHP Version: 7.3.11
Block user comment: N
Private report: N
New Comment:
Of course the minute after I send that I figure it out.
The reference mattered because ++$a incremented $a and then "returned" $a. In other words,
++$a;
++$a;
echo ($a)+($a);
When PHP 7 changed references and introduced AST and redid everything else, that nuance disappeared
and the expression would properly return the *value of* $a, regardless of whether the variable was a
reference or not.
While I don't remember a specific example, I know there have been a few bug reports about this
same change in behavior with similar situations. I might be able to find one...
Previous Comments:
------------------------------------------------------------------------
[2019-11-18 16:27:20] requinix@php.net
Sorry yes, you're right, it's a pre-increment in there, and the reference does (did)
matter.
5 is the correct output - I'm not sure how it came up with 6 before.
------------------------------------------------------------------------
[2019-11-18 16:22:23] cmb@php.net
> It's about the undefined execution order.
I don't think so, since it doesn't matter whether (++$a) is
evaluated before (++$a) or the other way round. It rather
seems to me that PHP < 7 got confused by the reference.
------------------------------------------------------------------------
[2019-11-18 15:12:35] requinix@php.net
It's about the undefined execution order.
https://www.php.net/manual/zh/language.operators.precedence.php
> Operator precedence and associativity only determine how expressions are grouped, they do not
> specify an order of
> evaluation. PHP does not (in the general case) specify in which order an expression is
> evaluated and code that
> assumes a specific order of evaluation should be avoided, because the behavior can change
> between versions of PHP
> or depending on the surrounding code.
>
> Example #2 Undefined order of evaluation
<?php
$a = 1;
echo $a + $a++; // may print either 2 or 3
$i = 1;
$array[$i] = $i++; // may set either index 1 or 2
?>
(the page is already marked as needing a translation update)
------------------------------------------------------------------------
[2019-11-18 13:11:13] cmb@php.net
Isn't 5 the output one would expect?
------------------------------------------------------------------------
[2019-11-18 09:35:47] 1003674174 at qq dot com
Description:
------------
php5.6echoçå¼æ¯6ï¼php7çå¼æ¯5
Test script:
---------------
$a=1;$b=&$a;echo (++$a)+(++$a);exit;
------------------------------------------------------------------------
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Edit this bug report at https://bugs.php.net/bug.php?id=78829&edit=1
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