Description:
------------
As stated at http://php.net/manual/en/function.curl-close.php an invocation to curl_close($ch) will 

"Closes a cURL session and frees all resources. The cURL handle, ch , is also deleted. "

However, it does not.

Curl seems to work differently than other functions that produce a resource as well. Curl does not pass by reference implicitly

For example:

// create an image resource
$image = imagecreate(100, 100);
$im = new stdClass();
$im->res = $image; // pass by reference
var_dump($image);
var_dump($im->res);
imagedestroy($image);
var_dump($image); // will print resource(4) of type (Unknown)
var_dump($im->res); // will print resource(4) of type (Unknown)

After calling imagedestroy($image), $image and $im->res are deleted



Reproduce code:
---------------
$s = curl_init();
$im = new stdClass();
$im->res = $s; // resource is passed by reference
var_dump($s); // will print: resource(5) of type (curl) 
var_dump($im->res); // will print: resource(5) of type (curl)
curl_close($s);
var_dump($s);
var_dump($im->res);

Expected result:
----------------
$s = curl_init();
$im = new stdClass();
$im->res = $s; // resource is passed by reference
var_dump($s); // will print: resource(5) of type (curl) 
var_dump($im->res); // will print: resource(5) of type (curl)
curl_close($s);
var_dump($s); // (expected): resource(5) of type (Unknown)
var_dump($im->res); // (expected): resource(5) of type (Unknown)

Actual result:
--------------
$s = curl_init();
$im = new stdClass();
$im->res = $s; // resource is actually passed by value
var_dump($s); // will print: resource(5) of type (curl) 
var_dump($im->res); // will print: resource(5) of type (curl)
curl_close($s);
var_dump($s); // (actual): resource(5) of type (curl)
var_dump($im->res); // (actual): resource(5) of type (curl)

$s becomes invalid but $im->res is still valid for subsequent operations.