Rename AxisExpr and axis_expr?

[grothesque]

While introducing mdarray to a new user within our research group, the topic of iterating over the hyperplanes of an array came up. The functionality is there (method axis_expr), but we have the impression that this name is not clear, and also does not fit well with lanes, cols, rows.

A name that fits better and is clearer might be “hyperplanes” or “planes”.

A separate question: What is the reason that Expression is implemented for View and ViewMut rather than for &Slice and &mut Slice?

[fre-hu]

The naming of these follow the ones in ndarray with expr instead of iter. There is a similar method outer_expr for the first dimension. To get contiguous views, the dimension must be Const<0> and not 0 so outer_expr is convenient to have.

A drawback with planes is that it is usually 2D, so hyperplanes is more correct (but longer). An alternative is slices that is similar to eachslice in Julia. For outer_expr then maybe subslices or subplanes.

I'm not sure though, it is also good to be close to ndarray.

I thought of implementing Expression for &Slice and &mut Slice, but was afraid of confusion which methods are called. For example array.map(...) uses the one in Array while (*array).map(...) the one in Expression. Other methods in Expression that don't exist in Array can be used directly. Another reason is that View is modified during iteration but could be avoided. It would be convenient to access Expression directly though.