Missing ampersand when passing byref

[radekm]

I wanted to load string to Vector256 so I initially wrote

let s = "Hi, what's your name?"
let span = s.AsSpan()
let r = &MemoryMarshal.GetReference(span)
let v = Vector256.LoadUnsafe<uint16>(Unsafe.As(&r))  // <== & should precede Unsafe.As.

It throws System.NullReferenceException. Then I realized that & is missing before Unsafe.As. But now I'm wondering why it even compiles (it seems I'm giving uint16 where byref<uint16> is expected)?

Following doesn't compile as expected:

let r2 : byref<uint16> = &Unsafe.As(&r)
let v2 = Vector256.LoadUnsafe<uint16>(r2)  // <== Doesn't compile (& should precede r2).

[T-Gro]

As far as I can see in https://sharplab.io/#v2:EYLgxg9gTgpgtADwGwBYA0AbEAzAzgHwgAcYA7AAgGUBPXAFxgFsA6AJQFdS6BLRmZgJJcYUYpREA3bmBi4AsAChiZKrQYsOXXvyF0o3UrmnylJCjXpM2nHn2YBhCIyLcMI8VCkyTy82qaKgQpudOSM1ABinGDkABQAlOQAvOSK5OnkIeS4yeQARAAS3GjkAO4AFgCGdADkOdQQ7FDkpJV8APx5aRlZuESVFCm4zACCuJT9pAnd6VnNKQBkALJM0NRLlVC4VRjMAOIwdKww2CJkMrF9A/EzmYfkErkAajBgdNAATACsSMwAMhBKgATACqhkqpwAPOwDHQAIxIAB8sTBuAh/DGsQWUHiiQyt0chggbmYAHV9Aw/gYYLEJPtDgAVagkBLMBkQSh6AwAcwSNwUQSBEDCkWiCSAA , the compiler did generate the ref for you in this case.