[PHP-BUG] Req #67847 [NEW]: add language construct is_ref() and refcount()

From:             ky dot patterson at adlinkr dot com
Operating system: 
PHP version:      Irrelevant
Package:          PHP Language Specification
Bug Type:         Feature/Change Request
Bug description:add language construct is_ref() and refcount()

Description:
------------
Userland developers do not have any way to determine whether a variable
(a zval) is a reference, or to return its reference count.

Function var_dump() shows is_ref.
Function debug_zval_dump() shows is_ref and refcount.
However both functions have severe limitations:
1) both functions output string data, requiring a developer to use
output buffering and string parsing/PCRE to extract the info;
2) since PHP 5.4 calltime pass-by-reference is gone, and neither
function is declared to pass-by-reference so both functions cannot be
made to handle references properly even for cases where the developer
knows the value is a reference;
3) "fixing" either function to use pass-by-reference doesn't really
solve the problem, because the zval will still be altered or copied by
the act of being passed as a function argument. By definition, no
function can read an unaltered zval.

The Xdebug extension offers xdebug_zval_dump() which does show accurate
info, but also has problems:
1) it can't reference all possible variables;
2) it's a non-standard extension, it isn't even on PECL.


As far as I can see, the solution (if there is to be one) is to add new
language constructs, similar to isset() or empty(); e.g.:

bool is_ref(mixed $var)
    Return whether PHP variable $var is a reference.
    (In other words, return $var's zval's is_ref__gc as a boolean.)

int getrefcount(mixed $var)
    Return the reference count of PHP variable $var.
    (In other words, return $var's zval's refcount__gc as an int.)


So there are several questions for the PHP core community to consider
here, IMO:

1) Am I correct in my assertion that only new language constructs could
provide this info for userland devs?

2) Is it technically feasible to implement these new language
constructs?
I am a novice zend hacker at best, I've never read the C code for e.g.
empty() so I don't know what's involved.

3) Is it actually worthwhile to provide this feature?
I think there is good value but I'm just this guy (and I'm not providing
a patch to implement it).
I acknowledge that it's a valid question -- I just think it should be
answered conclusively so the community knows the deal.


Lastly, I found several other bugs (some open) that are essentially
asking for this feature but as a new or improved function (with various
comments about how that won't work):
https://bugs.php.net/bug.php?id=40011 Request for refcount function
https://bugs.php.net/bug.php?id=52215 Add var_ref_count()
https://bugs.php.net/bug.php?id=66455 Missing function to determine
refcount of variables directy
https://bugs.php.net/bug.php?id=53895 debug_zval_dump should be by ref


Test script:
---------------
// Example script illustrating new language constructs:

$a = 1;
$b = $a;
$c = $b;
$d = 2;
$e =& $d;

if (is_ref($a))
    echo "\$a is a reference\n";
else
    echo "\$a is not a reference\n";
echo "\$a refcount is " . getrefcount($a) . "\n";

if (is_ref($d))
    echo "\$d is a reference\n";
else
    echo "\$d is not a reference\n";
echo "\$d refcount is " . getrefcount($d) . "\n";


Expected result:
----------------
$a is not a reference
$a refcount is 3
$d is a reference
$d refcount is 2

Actual result:
--------------
Feature doesn't exist, it is not possible to write code to produce any
result

-- 
Edit bug report at https://bugs.php.net/bug.php?id=67847&edit=1
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