elementPtr method
Address of element index in the array pointed to by this pointer,
given the address of the pointer slot (fieldPtr). Dereferences
fieldPtr for you, then delegates to elementPtrFrom.
For T* p, this is p[index], i.e. *fieldPtr + index * sizeof(T).
Implementation
MemoryPointer<R> elementPtr(MemoryPointer fieldPtr, int index)
=> elementPtrFrom(deref(fieldPtr), index);