Description:
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I can only use function test ($x = "Hello") {}

I wish to be able to use also variables to define a default value of a function variable like function test ($x = $_SESSION["value"]) {}

If the default-variable doesn't exist and the function isn't called with a parameter, PHP should output a notice that the default variable doesn't exist and assume that it would be NULL.

Test script:
---------------
<?php
function test ($x = $GLOBALS["print"]) { var_dump($x); } // or maybe ($x = $print) ?
$print = "Hello";
test("Bye"); // should output string(3) "Bye"
test(); // should output string(5) "Hello" (the value of $GLOBALS["print"])
$print = "Hi";
test(); // should output string(2) "Hi" (the actual value of $GLOBALS["print"])
unset($print);
test(); // should throw a notice "Undefined index: print" and output NULL
?>

or for a method in a class

<?php
class x
{
public $print = "Hello"
function test ($x = $this->print) { print $x; }
}
$x = new x;
$x->test("Bye"); // should output "Bye"
$x->test(); // should output "Hello" (the value of $x->print)
?>