Yesterday I was window shopping for new computer languages and I found rust which looks awesome if not yet mainstream. I like array-based approaches to certain problems, so I checked for ndarray support and found this github library. Nice!

Anyway, I noticed that this crate uses u32 for indexing.
http://bluss.github.io/rust-ndarray/doc/ndarray/struct.Array.html
In numpy it is increasingly common for users to have large arrays that cannot be indexed by such small integer types. I personally don't have enough RAM for this, but this could change in the future. Or you might want the same interface for arrays on disk as in RAM, or the same interface for sparse arrays that could more easily hold more entries. But of course using unnecessarily large integer types for indexing slows the code and increases the memory usage...