Well, the point is safety for existing code. If you can annotate pointers to match them with their bound you can as easily replace them with a span and avoid ne

Well, the point is safety for existing code. If you can annotate pointers to match them with their bound you can as easily replace them with a span and avoid needing compiler heroics. Edit: unless you absolutely need the change to be ABI stable, but even then there are ways around that.