Question

Have anyone had an experience in converting ref byte into byte[]?

If the function takes an argument like

void foo(ref byte buffer);

then it is possible to call foo using

void call_func()
{
    byte arr[] = new byte[10];
    foo(ref arr[0]);
}

The question is how can one re-convert the buffer argument into byte[] array in the foo.

Answer 1

You don’t.

In order to avoid pinning the entire array, the runtime might just make a copy of the single element you selected (and then copy back after the call). In that case your function will get the address of a temporary copy, which is unrelated to the address of the other array elements. (Well, there could be some aliasing considerations, this optimization is much more likely for pinvoke and/or remote calls, where aliasing analysis is more feasible)

If you need an array, pass the array.

---

If you don’t care that it might not work right, you can use unsafe code to get to the other elements.

pinned( byte* p = &buffer ) {
    buffer[4] = 0;
}