I would like a simpler way to create a SliceArg that matches an arbitrary Dimension

[insideoutclub]

The code below is my solution for Advent Of Code 2020 Day 17. The problem involves running Conway's Game of Life in both 3 and 4 dimensions. I want to use slice_mut to create a mutable slice for Dimension D. The only way I could figure out how to do it was to convert the array to IxDyn using into_dimensionality, slice the array using a Vec I created, and then convert the array back to dimension D.

To solve a similar problem, I was able to call raw_dim on my existing array, and then iterate over it and modify it. My initial proposal would be to have a similar method (raw_slice?) that would return a SliceArg that I could then iterate over and modify in place.

https://play.rust-lang.org/?version=stable&mode=release&edition=2018&gist=4a028d474bec27d8f32f938ece81b0e4

[jturner314]

I think the simplest way to implement the slicing in the example would be like this:

let mut v = x.view_mut();
field
    .axes()
    .for_each(|ax| v.slice_axis_inplace(ax.axis(), Slice::from(2..2 + ax.len())));
v.assign(field);

This doesn't require x to be dynamic-dimensional.

Usually, the simplest way to perform slicing in a function which is generic over dimensionality is to use the methods which slice individual axes, like .slice_axis_inplace() and .collapse_axis(). I've created #912 to improve the documentation in this area.

[insideoutclub]

That's a lovely solution. Thank-you.

[jturner314]

When the next version of ndarray is released, the slicing in the example will be able to be implemented like this:

x.slice_each_axis_mut(|ax| Slice::from(2..2 + field.len_of(ax.axis()))).assign(field);

(See PR #913.)