Struct Direction 

pub struct Direction {
    pub name: &'static str,
    pub dx: i64,
    pub dy: i64,
}

One direction of a neighbourhood record: the field’s name and the (dx, dy) step it names.

Name and offset are one tuple on purpose. Two parallel lists — field names here, offsets in the wrapper — is exactly the shape that lets slot i hold the neighbour of direction j, which no test of either list alone would catch.

Fields

name: &'static str

The record field’s name, and therefore the schema’s slot at this index.

dx: i64

Column step. y grows downward, so down is +1.

dy: i64

Row step.