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 }

Ok, now I think I understand what's going on here. In the StructView approach, cursors can only point to instances of struct types. Which means that if you want to iterate over fixed-length, uniform data, you have to write it out as a struct, rather than using an array.

But this raises the question of why nominal typing is ok for structs but not for arrays, since we've just seen that they're interchangeable here. We could structurally type structs, in which case StructView has exactly the same perf costs, or we could nominally type arrays, so everything is fast even in the PointerType version. Right?

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

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.