use Data::Dump qw(dump);

my @dna = qw(A T T G C);

print +(dump \@dna),$/;

my @view;
make_view( \@dna, 1, \@view, 0 );
make_view( \@dna, 2, \@view, 1 );

#mutate

$view[0] = 'x';
$view[1] = 'x';

print +(dump \@dna), $/;

make_view( \@dna, 4, \@view, 0 );

print +(dump \@dna), $/;

# print ["A", "T", "x", "G", "x"]

sub make_view {
    my ($arr, $idx1, $view, $idx2) = @_;
    tie $view[$idx2], 'Overridden', sub : lvalue { $arr->[$idx1] };
    return;
}

{
    package Overridden;

    sub TIESCALAR {
        my ($class, $item) = @_;
        return bless \$item, $class;
    }

    sub FETCH {
        my $self = shift;
        ${$self}->();
    }

    sub STORE {
        my $self = shift;
        my ($val) = @_;
        ${$self}->() = $val;
    }
}