Here's another tied variable solution. I didn't implement most of the tied array methods; it's ill-defined what push, pop, etc. should do in this case.

All told, I think I prefer your solution after blokhead's suggestions.

package Array::AliasRange;

sub TIEARRAY {
    my ($class, $array, $offset, $length) = @_;
    bless {
    array => $array,
    offset => $offset,
    length => $length,
    }, $_[0];
}

sub _real_index {
  my ($self, $index) = @_;
  if ($index >= 0) {
    return undef if ($index + $self->{offset}) >= ($self->{offset} + $
+self->{length});
    return $index + $self->{offset};
  } else {
    return undef if (scalar @{$self->{array}} - ($index + $self->{offs
+et})) < 0;
    return scalar @{$self->{array}} - ($index + $self->{offset});
  }
}

sub FETCH {
  my ($self, $index) = @_;
  my $real_index = _real_index($self, $index);
  return defined $real_index ? $self->{array}[$real_index] : undef;
}

sub STORE {
  my ($self, $index, $newval) = @_;
  my $real_index = _real_index($self, $index);
  return defined $real_index ? ($self->{array}[$real_index] = $newval)
+ : undef;
}

sub FETCHSIZE {
  my $self = shift;
  return $self->{length};
}

package main;

sub by_groups_of {
  my ($by, $arrayref) = @_;
  return sub { () } if ! $by || $by =~ /\D/ || ! @$arrayref;
  my $offset = 0;
  return sub {
    return () if $offset >= scalar @$arrayref;
    my @new_array;
    my $length = ($offset + $by >= scalar @$arrayref) ? (scalar @$arra
+yref - $offset) : $by;
    tie @new_array, "Array::AliasRange", $arrayref, $offset, $length;
    $offset += $by;
    return \@new_array;
  }
}


my @array = 0 .. 10;
my $next = by_groups_of( 3, \@array );

while ( my $group = $next->() ) {
  $group->[1] = 'foo';
}
print join ' ', @array, "\n";
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