Why `Substring` cannot make a reference to the original data instead of a copy? about referencesource HOT 1 OPEN

This repo is not very active, so it's not a great place to ask questions like this. A better choice would be the repo for the modern .Net runtime: dotnet/runtime.

That being said, what you're saying would require changing the structure of the string type, which is a pretty fundamental part of the runtime. Instead, .Net decided to add the Span<T> type, which can represent any memory sequence, which means the equivalent operation to Substring, called Slice, works exactly the way you want there.

from referencesource.