I don't think I understand the difference between "# another way, since @_ is an alias:"

In Perl, everything is passed by reference. To avoid confusion with Perl references — an unrelated concept — this is known as "aliasing" in the Perl world.

When a function is called, the elements of @_ are aliased to the arguments in the caller. Changes to @_ will be reflected in the arguments passed to the function.

In the following snippet, $_[0] is aliased to $x, and $_[1] is aliased to $y. Notice how changing @_ changed $x and $y, and notice how no references — and no dereferencing — were used.

sub func {
   print("f-pre:  $_[0], $_[1]\n");
   $_[0] = 5;
   $_[1] = 6;
   print("f-post: $_[0], $_[1]\n");
}

my $x = 3;
my $y = 4;
print("pre:    $x, $y\n");
func($x, $y);
print("post:   $x, $y\n");
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pre:    3, 4
f-pre:  3, 4
f-post: 5, 6
post:   5, 6
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