There are interesting differences in these types worth thinking about if you're imagining try to standardize them somehow.
C++ std::span pulls double duty, one flavour of std::span, the one you might see more often, is like Rust's slice type [T] in that it consists of zero or more values of some type T. The other though is more like Rust's array type [T; N] where the size N of the span is actually part of the type itself.
Rust's slice is specifically that [T] type, the type system doesn't see any more difference between a [u32] with 1000 entries and a [u32] with 0 entries than it would between a string with "DOG" in it and a string with "CAT" in it, their types are identical.
C# Span<T> deliberately can't live on the heap. The CLR doesn't want to cope with this type, and by ensuring it's part of your program's stack any questions about the lifetime of the Span are obviated and tricky-to-reason about garbage collection problems don't arise.
Go's slices are very strange because Go's arrays are like those in Rust, their size is part of their type - and yet Go's slices can append. This is achieved by actually creating a new array and copying all the data for the slice into the new array whenever Go sees fit.
C++ std::span pulls double duty, one flavour of std::span, the one you might see more often, is like Rust's slice type [T] in that it consists of zero or more values of some type T. The other though is more like Rust's array type [T; N] where the size N of the span is actually part of the type itself.
Rust's slice is specifically that [T] type, the type system doesn't see any more difference between a [u32] with 1000 entries and a [u32] with 0 entries than it would between a string with "DOG" in it and a string with "CAT" in it, their types are identical.
C# Span<T> deliberately can't live on the heap. The CLR doesn't want to cope with this type, and by ensuring it's part of your program's stack any questions about the lifetime of the Span are obviated and tricky-to-reason about garbage collection problems don't arise.
Go's slices are very strange because Go's arrays are like those in Rust, their size is part of their type - and yet Go's slices can append. This is achieved by actually creating a new array and copying all the data for the slice into the new array whenever Go sees fit.