Neumann and Moore neighborhood calculation for rectangular grid

lib.rs

#[derive(Clone, Copy)]
pub struct Bounds {
    rows: usize,
    cols: usize,
}

type Pos = (usize, usize);

impl Bounds {
    pub fn around_neumann(
        self,
        buf: &mut [Pos; 4],
        (row, col): Pos
    ) -> &[Pos] {
        let mut i = 0;
        let mut put = |r, c| {
            buf[i] = (r, c);
            i += 1;
        };
        if let Some(row) = row.checked_sub(1) {
            put(row, col);
        }
        if let Some(col) = col.checked_sub(1) {
            put(row, col);
        }
        if col + 1 < self.cols {
            put(row, col + 1);
        }
        if row + 1 < self.rows {
            put(row + 1, col);
        }
        &buf[..i]
    }

    pub fn around_moore(self, buf: &mut [Pos; 8], (row, col): Pos) -> &[Pos] {
        let mut i = 0;
        let mut put = |r, c| {
            buf[i] = (r, c);
            i += 1;
        };
        if let Some(row) = row.checked_sub(1) {
            if let Some(col) = col.checked_sub(1) {
                put(row, col);
            }
            put(row, col);
            if col + 1 < self.cols {
                put(row, col + 1);
            }
        }
        if let Some(col) = col.checked_sub(1) {
            put(row, col);
        }
        if col + 1 < self.cols {
            put(row, col + 1);
        }
        if row + 1 < self.rows {
            let row = row + 1;
            if let Some(col) = col.checked_sub(1) {
                put(row, col);
            }
            put(row, col);
            if col + 1 < self.cols {
                put(row, col + 1);
            }
        }
        &buf[..i]
    }
}