{
        package Array::Grouped;

        sub TIEARRAY { bless { n => $_[1], array => $_[2] } => $_[0] }
        sub FETCHSIZE { @{$_[0]{array}} / $_[0]{n} }
        sub FETCH {
            my $self = shift;
            my ($i) = @_;
            my $n = $self->{n};
            return sub { \@_ }->(@{$self->{array}}[$i*$n .. $i*$n + $n - 1]);
        }
    }

    my @bar = 0 .. 9;
    tie my @foo, Array::Grouped::, 2, \@bar;

    for (@foo) {
        $_->[0] = 'x';

    }

    print @bar; # x1x3x5x7x9


    ### Update:

    sub by_groups_of { tie my @foo, Array::Grouped::, @_ }

    my $foo = by_groups_of(2, \@bar);

    for (@$foo) {
        $_->[0] = 'y';
    }

    print @bar; # y1y3y5y7y9