.NET Length UInt64, Span etc

[Xyncgas]

Since processors are 64 bit, why not use UInt64 by default on things like length of IEnumerable

[Clockwork-Muse]

1. (Massive) Breaking change
2. There's some debate over whether sizes should be unsigned at all (due to conversion rules, among other things).
3. In any real-world application it's unlikely to be practical to iterate over that many elements in an IEnumerable. Getting a 2GB+ contiguous span of memory (for an array or similar) is barely supported.

[huoyaoyuan]

Se also the discussion in #12221

[Xyncgas]

Thanks for the infos