Are you familiar with integer division and modulus? There is a very simple trick for converting between flat indices into your Vec and (row, col) pairs.
Assuming data is ordered so that values of equal row are contiguous:
index = width * row + colcol = index % widthrow = index / width
With this, you do not need a Cell type, because you can easily recover row and col from an index. Here is a wrapper type which makes use of these relationships. Try working with a Grid<Enum>:
struct Grid<T> {
dim: (usize, usize),
data: Vec<T>,
}
type Pos = (usize, usize); // written as (row, column)
impl<T> Grid<T> {
pub fn new(dim: (usize, usize), data: Vec<T>) -> Self {
assert_eq!(dim.0 * dim.1, data.len());
Grid { dim, data }
}
fn flat_index(&self, pos: Pos) -> usize {
assert!(pos.0 < self.dim.0);
assert!(pos.1 < self.dim.1);
let strides = (self.dim.1, 1);
pos.0 * strides.0 + pos.1 * strides.1
}
// inverse of flat_index
fn pos(&self, index: usize) -> Pos {
(index / self.dim.1, index % self.dim.1)
}
pub fn at_pos(&self, pos: Pos) -> &T {
&self.data[self.flat_index(pos)]
}
}
Such a helper type could expose methods for viewing neighbors as follows:
impl<T> Grid<T> {
pub fn neighbors(&self, pos: Pos) -> Vec<&T> {
let mut out = Vec::with_capacity(4);
self.each_neighbor_pos(pos, |neighbor| {
out.push(self.at_pos(neighbor));
});
out
}
// helper, written in the form of an "internal iterator" to make it
// easier to add other things (like e.g. a `neighbors_mut` function)
fn each_neighbor_pos(&self, pos: Pos, mut func: impl FnMut(Pos)) {
if pos.0 != 0 {
func((pos.0 - 1, pos.1));
}
if pos.1 != 0 {
func((pos.0, pos.1 - 1));
}
if pos.0 + 1 != self.dim.0 {
func((pos.0 + 1, pos.1));
}
if pos.1 + 1 != self.dim.1 {
func((pos.0, pos.1 + 1));
}
}
}
Note that several popular third-party implementations of my Grid type already exist if you are interested. See:
-
ndarray, a generalization to n dimensions which also works with discontiguous data. (this is on the "complicated but powerful" end!)
-
imgref, which despite the name is not just for images! I've never used it but I know it provides a 2D type much like my Grid (as well as "grid views" for viewing a region of the grid), and is probably easier to learn than ndarray.
