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Bug #64248 Strange parse error when using language construct in for
Submitted: 2013-02-19 21:03 UTC Modified: 2013-02-20 08:06 UTC
From: bobwei9 at hotmail dot com Assigned:
Status: Not a bug Package: Scripting Engine problem
PHP Version: master-Git-2013-02-19 (Git) OS: Irrelevant (OS X 10.8)
Private report: No CVE-ID: None
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 [2013-02-19 21:03 UTC] bobwei9 at hotmail dot com 
Description:
------------
For example unsetting a var in the third part of a for-loop throws an E_PARSE error.

Test script:
---------------
php -r '
$A = [1];
$B = [1,7];
$max = 'B';
for ($i='A'; ++$i<$max; unset($$i))
var_dump($$i);'


Expected result:
----------------
array(1) {
  [0]=>
  int(1)
}
array(2) {
  [0]=>
  int(1)
  [1]=>
  int(7)
}

Actual result:
--------------
PHP Parse error:  syntax error, unexpected 'unset' (T_UNSET), expecting ')' in Command line code on line 1

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 [2013-02-19 21:05 UTC] bobwei9 at hotmail dot com 
Oops, the expected result should be a notice and $max should be 'A' in the test script...
 [2013-02-19 23:46 UTC] johannes@php.net
-Status: Open +Status: Not a bug
 [2013-02-19 23:46 UTC] johannes@php.net 
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

unset() jsut as many other language constructs has no return value and is no expression. for expects expressions. This construct makes sense only in very few cases, even though it might make the language a tiny bit simpler (less exceptions) it is not worth changing the language ... (changing language has effects for the whole environment, from IDEs to code analyzers, to ...)
 [2013-02-20 08:06 UTC] bobwei9 at hotmail dot com 
It is a language construct, yes. But this seems to be a design mistake which should not be.

As in the pull request proposed:  "an idea would be to make unset return true if the variable has 
existed else false?"

Does this need a RFC or a discussion on the internals?
 [2013-02-20 22:50 UTC] nikic@php.net 
Imho unset() should stay as it is, a statement. It has no meaningful return value and does not really benefit much from allowing expression use.

If you want to perform some complex operation in the last for-loop expressions, then you should just put it into the body:

    for ($i = 'A'; ++$i < $max;) {
        var_dump($$i);
        unset($$i);
    }

The last for-loop expression is usually used for variable increments or other simple expressions. It's not there to inline your whole loop body. If you want to put your unset() call in there, why not move the var_dump in there too?

    for ($i = 'A'; ++$i < $max; var_dump($$i), unset($$i));

Look, it's shorter!

Just my opinion on this.
 
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