pointer type approach

example.js

var IPAddress = new ArrayType(uint8, 4);
var P_IPAddress = new PointerType(IPAddress);

var Packet = new StructType({ addr: IPAddress, ... });
var P_Packet = new PointerType(Packet);

var PacketArray = new ArrayType(Packet);
var lotsOfPackets = new PacketArray(LOTS);

for (let p of lotsOfPackets.cursor("addr")) {
    ...
}

pointer-type.txt

+-------------+           +-----------------------+
|             |---------->|                       |
| PointerType |           | PointerType.prototype |
|             |<----------|                       |
+-------------+           +-----------------------+
                                      ^
                                      |
                                      |
                          +-----------------------+           +-------------+
                          |                       |---------->|             |
                          | T                     |           | T.prototype |
                          |                       |<----------|             |
                          +-----------------------+           +-------------+
                                                                     ^
                                                                     |
                                                                     |
                                                              +-------------+
                                                              |             |
                                                              | p           |
                                                              |             |
                                                              +-------------+

types.txt

b ::= int8 | uint8 | int16 | uint16 | int32 | uint32 | float32 | float64

t ::= b | s | *s
s ::= [t x k] | { x1: t1, ..., xn: tn }

The issue is just that it seems stranger for different array types to be non-interchangeable than for different struct types, right?

Right.

But more broadly, it also violates expectations if updating a pointer involves an O(n) check (where n is the size of the type, not the data structure, but still). So I really wanted to avoid structural type checks.