Also will throw in to the mix, in C#: https://julesjacobs.com/2014/11/11/immutable-vectors-csharp.html https://julesjacobs.com/2014/11/11/immutable-vectors-csh

Also will throw in to the mix, in C#: https://julesjacobs.com/2014/11/11/immutable-vectors-csharp.html https://julesjacobs.com/2014/11/11/immutable-vectors-csharp.... His implementation uses buffers of capacity 32, generics, and bit shifting to do lookups.