Using Box<[T]> in Rust for multi-dimensional arrays

playground.rs

use std::{fmt, ops};

pub struct Array2D<T> {
    width: usize,
    height: usize,
    data: Box<[T]>,
}

impl<T> Array2D<T> {
    pub fn new(size: (usize, usize)) -> Self
        where T: Default
    {
        let (width, height) = size;
        assert_ne!(width, 0);
        assert_ne!(height, 0);
        let size = width.checked_mul(height).expect("Array of this size would not fit into memory");
        let mut vec = Vec::with_capacity(size);
        vec.extend(std::iter::repeat_with(T::default).take(size));
        let data = vec.into_boxed_slice();
        Array2D {
            width,
            height,
            data,
        }
    }

    pub fn width(&self) -> usize { self.width }

    pub fn height(&self) -> usize { self.height }

    pub fn len(&self) -> usize {
        //  probably faster than multiplication
        self.data.len()
    }

    fn make_index(&self, xy: (usize, usize)) -> usize {
        let (x, y) = xy;
        assert!(x < self.width);
        assert!(y < self.height);
        y * self.width + x
    }

    pub fn column(&self, column_index: usize) -> Column<T> {
        assert!(column_index < self.width());
        Column::new(self, column_index)
    }

    pub fn columns<'a>(&'a self) -> impl Iterator<Item=Column<'a, T>> + 'a {
        (0..self.width()).map(move |x| self.column(x))
    }

    pub fn row(&self, row_index: usize) -> Row<T> {
        assert!(row_index < self.height());
        Row::new(self, row_index)
    }

    pub fn rows<'a>(&'a self) -> impl Iterator<Item=Row<'a, T>> + 'a {
        (0..self.height()).map(move |y| self.row(y))
    }
}

impl<T> ops::Index<(usize, usize)> for Array2D<T> {
    type Output = T;
    
    fn index(&self, xy: (usize, usize)) -> &T {
        let index = self.make_index(xy);
        &self.data[index]
    }
}

impl<T> ops::IndexMut<(usize, usize)> for Array2D<T> {
    fn index_mut(&mut self, xy: (usize, usize)) -> &mut T {
        let index = self.make_index(xy);
        &mut self.data[index]
    }
}

impl<T> fmt::Display for Array2D<T>
    where T: fmt::Display
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        "Array2D([\n".fmt(f)?;
        for row in self.rows() {
            "  [".fmt(f)?;
            for (x, item) in row.enumerate() {
                write!(f, "{}", item)?;
                if x != (self.width() - 1) {
                    ", ".fmt(f)?;
                }
            }
            "]\n".fmt(f)?;
        }
        "])".fmt(f)?;
        Ok(())
    }
}

pub struct Row<'a, T> {
    array: &'a Array2D<T>,
    row: usize,
    current_column: usize,
}

impl<'a, T> Row<'a, T> {
    pub fn new(array: &'a Array2D<T>, row: usize) -> Self {
        assert!(row < array.height);

        Row {
            array,
            row,
            current_column: 0
        }
    }

    pub fn current_column(&self) -> usize {
        self.current_column
    }
}

impl<'a, T> Iterator for Row<'a, T> {
    type Item = &'a T;
    
    fn next(&mut self) -> Option<&'a T> {
        if self.current_column >= self.array.width() {
            None
        } else {
            let index = (self.current_column, self.row);
            let item = &self.array[index];
            self.current_column += 1;
            Some(item)
        }
    }
}

pub struct Column<'a, T> {
    array: &'a Array2D<T>,
    column: usize,
    current_row: usize,
}

impl<'a, T> Column<'a, T> {
    pub fn new(array: &'a Array2D<T>, column: usize) -> Self {
        assert!(column < array.width);

        Column {
            array,
            column,
            current_row: 0
        }
    }

    pub fn current_row(&self) -> usize {
        self.current_row
    }
}

impl<'a, T> Iterator for Column<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<&'a T> {
        if self.current_row >= self.array.height() {
            None
        } else {
            let index = (self.column, self.current_row);
            let item = &self.array[index];
            self.current_row += 1;
            Some(item)
        }
    }
}

fn incremental_array(size: (usize, usize)) -> Array2D<u8> {
    let mut array = Array2D::new(size);
    let mut item = 0u8;
    for x in 0..array.width() {
        for y in 0..array.height() {
            array[(x, y)] = item;
            item += 1;
        }
    }
    array
}

fn main() {
    let a = incremental_array((10, 15));
    println!("{}", a);
}

rust playground permalink:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=01a32331d7a2dd71a0ad8d1babc0c170