Globals, closures, and filter_input

This seems to me to be an odd combination and it is not explictly
documented.

I'm running under PHP 5.5.12

First off, when after executing unset($_GET) - the global $_GET variable
no longer exists. However, calling filter_input(INPUT_GET,...)
continues to return data from the query string.

So filter_input and filter_has_var are independent of the $_GET
variable. IE they will return whatever the original data was. This is
noted in the comments regarding these functions,
http://us1.php.net/manual/en/function.filter-input.php - I simply want
to double check that this is working as designed, and not a bug that
will be corrected[since there is no spec for this feature. :-)]

Moreover, it is possible to bind a closure to a global variable, for
example:

https://gist.github.com/garyamort/c656846ba3969c492d20

In this code, I bind a closure which returns the results of
filter_input(INPUT_GET,...) to the $_GET super global.

This was simply a quick and dirty exercise dynamically enabling $_GET
variable filtering in a manner which integrates nicely with most
introductory PHP tutorials.

A more thorough solution would be to instead create an ArrayObject
subclass and map the various array methods to the appropriate
filter_input and filter_has_var functions.

In that way, 'legacy' code could have it's input automatically
sanitized, with the ability to change the type of sanitization which
occurs during execution[since the current default sanitzation ini
setting can not be changed dynamically]

However, global variables are not supposed to be bound to closures and
objects, then this could result in future problems if that feature is
ever modified.