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Request #24116 Enhancement: extract() takes array of keys
Submitted: 2003-06-10 12:16 UTC Modified: 2014-04-16 18:44 UTC
Votes:1
Avg. Score:1.0 ± 0.0
Reproduced:0 of 0 (0.0%)
From: kop at meme dot com Assigned: levim (profile)
Status: Wont fix Package: *General Issues
PHP Version: * OS: Any
Private report: No CVE-ID: None
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From: kop at meme dot com
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 [2003-06-10 12:16 UTC] kop at meme dot com
I want to get variables passed from the client into local (not global) variables.  If the variable has not been passed from the client I do not want a local variable defined.  While this can be coded for each variable I want to do this with, there is no way to abstract this operation into a function.

The (untested) code to get a form variable 'foo' would be:

if (array_key_exists($_POST, 'foo') {
  $foo = &{$_POST['foo'])}
}
// $foo may or may not be defined, so if I've got strict
// error checking on I get a nice error if I ref an undefined
//variable.  And, $foo is nice and local so it won't show
// where I don't send it.

If extract() took an array of keys as another argument, extracting only those keys that are in the list, I could get the form variables, foo, bar, and baz with:

extract($_POST, EXTR_REFS, '', array('foo', 'bar', 'baz'));

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 [2003-06-10 21:37 UTC] kop at meme dot com
There is a glitch in my proposal, what if (in my example) there is no user supplied value for $foo, in that case if my program assigns a value to $foo, that value is local.  But, if the user does supply a value for $foo, then $foo is a reference into $_POST, and the value can be seen elsewhere in the program.  It's not a happy circumstance to have the scope of a value depend upon the presence or absence of some data in a data structure.  It'd make for bugs.

This could be solved with another kludge, like so:

Instead of:

extract($_POST, EXTR_REFS, '', array('foo', 'bar', 'baz'));

do

extract($_POST
        , EXTR_REF_INITS
        , ''
        , array('foo' => 'mydefaultval'
                , bar => 'mydefaultval'
                , 'baz' => UNASSIGNED));

UNASSIGNED is new.  It is a php predefined constant containing the value you get if you reference a variable which has not had a value assigned to it.

EXTR_REF_INITS is a new extract_type.  It works like EXTR_REFS, but when the (new) array argument is present it will put key/value pairs into the first extract() argument iff the key does not already exist in the first argument.

Clear like mud? 

I can't say for certain my proposal for extract() is the best solution.  Any of it.  It does seem a little of an aftermarket bolt-on.  Not that there shouldn't be a solution to what I want to accomplish.
 [2014-04-16 18:34 UTC] levim@php.net
-Status: Open +Status: Closed -Package: Feature/Change Request +Package: *General Issues -Operating System: All +Operating System: Any -PHP Version: 4.3.2 +PHP Version: * -Assigned To: +Assigned To: levim
 [2014-04-16 18:34 UTC] levim@php.net
I agree that `extract` is the wrong approach. If you have a better idea, feel free to reopen the bug.
 [2014-04-16 18:44 UTC] levim@php.net
-Status: Closed +Status: Wont fix
 [2014-04-16 18:44 UTC] levim@php.net
I guess 'Closed' is for implemented features or fixed bugs. It is unclear what the correct option for 'declined for now' would be, so I am using Won't Fix.
 
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