I agree that it was not what was expected but it does fulfill the criteria as stated. The answer was probably supposed to be this as noted elsewhere:

$[

The index of the first element in an array, and of the first character
+ in a substring. Default is 0, but you could theoretically set it to 
+1 to make Perl behave more like awk (or Fortran) when subscripting an
+d when evaluating the index() and substr() functions. (Mnemonic: [ be
+gins subscripts.) 
As of release 5 of Perl, assignment to $[ is treated as a compiler dir
+ective, and cannot influence the behavior of any other file. --> Its 
+use is highly discouraged :-)


$[ = 1;
$x[0] = 1;
show();
$x[0] = 2;
show();
$x[1] = 3;
show();
sub show { print "\$x[$_] = $x[$_]\n" for 0..$#x; }
[download]

Yes, the answer was probably supposed to be this as noted elsewhere

As noted in the reply to that elsewhere, it's not the solution we were looking for. So if you're not all to disappointed yet, to achieve real insanity, try to find another solution.

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }

I agree that it was not what was expected but it does fulfill the criteria as stated.

No, as juerd pointed out, you're not changing $x[0] nor $x[1]: they both remain equal to \$_. All you show is that if you change ${$x[0]} then ${$x[1]} changes, which wasn't the exercise.

Note that I have no problem with unexpected solutions — I love the $[ one.. didn't think of that — but they do need to be valid.   :-)