sub foo {
    my $array_reference = shift;
    print "foo: ", $array_reference->[0], "\n";
}

sub bar (\@) {
    my $array_reference = shift;
    print "bar: ", $array_reference->[0], "\n";
}

my @a1 = ( 1 );
my @a2 = ( \@a1 );
my $a3 = [ 3 ];

foo(@a1);
foo(@a2);
foo($a3);

bar(@a1);
bar(@a2);
# bar($a3); # Can't do that because it would be a runtime error. 
bar(@$a3);