API design for communicating with network of heterogeneous devices

[lynaghk]

I'm designing a communications protocol for a chain of heterogeneous embedded devices (different sensors, etc.), but I'm not sure how to design an ergonomic API that's both:

• type-safe
• suitable for no-std usage (i.e., without dyn and allocations)

Conceptually things would compile down into something like:

let mut message = [0u8; A::Length + A::Length + B::Length];

//command device 1 (type A)
A::write_commmand(&mut message[0..1], A::Command::Foo);

//command device 2 (type A)
A::write_commmand(&mut message[1..2], A::Command::Bar);

//command device 3 (type B)
B::write_commmand(&mut message[2..4], B::Command::Baz);

let response = send(&message);

//read statuses
let d1: A::Status = A::read_status(&mut response[0..1]);
let d2: A::Status = A::read_status(&mut response[1..2]);
let d3: B::Status = B::read_status(&mut response[2..4]);

The topology (here, a chain of [A, A, B]) is known at compile-time, as are the status/command sizes.
Is it possible in Rust to define the topology once (in a function/macro invocation or data structure) and handle all of the buffer size and offset calculations behind the scenes?
Ideally the user-facing code would look something like:

let mut network = network![A, A, B];
network[0].write(A::Command::Foo);
network[1].write(A::Command::Bar);
network[2].write(B::Command::Baz);
send(&network.message);

let d1: A::Status = network[0].status;
let d2: A::Status = network[1].status;
let d3: B::Status = network[2].status;

I've tried to implement with

trait Device {
    type Message;
    const MESSAGE_LENGTH: usize;
}

but immediately run into object safety issues so figured I should ask for help to see if there are other patterns I should be exploring to solve this. Thanks!

[kornel]

To get multiple overlapping exclusive slices you need something like .split_at_mut(pos) (applied recursively) or .chunks(len).

let (first, rest) = message.split_at_mut(A::Length);
let (second, rest) = rest.split_at_mut(A::Length);
let (third, _) = rest.split_at_mut(B::Length);