Note that C#'s Memory<T> (a slice) isn't boxed either, but it stays memory-safe under tearing: the resulting slice might have unintended bounds, but it will either be in-bounds or will throw an exception.

This of course has some overhead, which is why you usually turn it into the cheaper, data race free Span<T>. Go could have the same safety and fix some of the overhead with compiler optimizations, they just don't want to take the trade-off.