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// `type Item = ..;` inside an `impl` binds a name the same block's signatures
// use as `Self::Item`. A `const` in an `impl` becomes a module-level constant
// named for both, since Nim has no per-type constant namespace.

struct Grid {
    cells: Vec<i32>,
    width: usize,
}

trait Cells {
    type Out;
    fn get_at(&self, i: usize) -> Self::Out;
    fn total(&self) -> Self::Out;
}

impl Cells for Grid {
    type Out = i32;

    fn get_at(&self, i: usize) -> Self::Out {
        self.cells[i]
    }

    fn total(&self) -> Self::Out {
        let mut t: i32 = 0;
        for c in self.cells.iter() {
            t += c;
        }
        t
    }
}

impl Grid {
    const BORDER: i32 = 7;

    fn at(&self, r: usize, c: usize) -> i32 {
        self.cells[r * self.width + c]
    }
}

fn main() {
    let g = Grid {
        cells: vec![1, 2, 3, 4, 5, 6],
        width: 3,
    };
    println!("{} {}", g.get_at(0), g.get_at(5));
    println!("{}", g.total());
    println!("{} {}", g.at(0, 2), g.at(1, 0));
    println!("{}", Grid::BORDER);
}