Variable variable Superglobals

Question

In PHP ...

var_dump(${'_GET'});   // array(0) { } - #1

$var = '_GET';
var_dump(${$var});     // array(0) { } - #2

function test() {
  var_dump(${'_GET'}); // array(0) { } - #3
  $var = '_GET';
  var_dump(${$var});   // NULL - #4
}
test();

What happen?

Answer 1

It's not a bug, it's a feature:

Warning

Please note that variable variables cannot be used with PHP's Superglobal arrays within functions or class methods. The variable $this is also a special variable that cannot be referenced dynamically.