How can bincode distinguish between tuples and (fixed size) arrays?

[jbe]

Continuing the discussion from Is it better to use bincode or postcard?:

// uses `bincode` version "2.0.0-rc.2"

fn main() {
    let tuple: (u16, u16) = (44, 55);
    let array: [u16; 2] = [44, 55];
    let stdcfg = bincode::config::standard();
    assert_eq!(bincode::encode_to_vec(&tuple, stdcfg).unwrap(), &[44, 55]);
    assert_eq!(bincode::encode_to_vec(&array, stdcfg).unwrap(), &[2, 44, 55]);
}

How can bincode distinguish between tuples and (fixed size) arrays? Aren't both going through the serde type tuple?

[H2CO3]

There's no 2.0 version of bincode. With the latest 1.3 version, the two data types serialize to the exact same representation.

[steffahn]

Seems like the bincode function in the code example doesn’t use serde, and there’s another one that does, treating arrays and tuples equally: Rust Explorer

[jbe]

---

@steffahn

Seems like the bincode function in the code example doesn’t use serde, and there’s another one that does , treating arrays and tuples equally: Rust Explorer

This means that the following code:

// uses `bincode` version "2.0.0-rc.2"

fn main() {
    let array: [u8; 3] = [11, 12, 13];
    let stdcfg = bincode::config::standard();
    assert_eq!(
        bincode::encode_to_vec(&array, stdcfg).unwrap(),
        bincode::serde::encode_to_vec(&array, stdcfg).unwrap(),
    );
}

Fails with:

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `[3, 11, 12, 13]`,
 right: `[11, 12, 13]`', src/main.rs:6:5

That's not good. This means bincode::encode_to_vec isn't compatible with bincode::serde::encode_to_vec. I don't think this is intended, is it?

@H2CO3

There's no 2.0 version of bincode.

Note I'm referring to version 2.0.0-rc.2, which is a published (non-yanked) release candidate.

[steffahn]

@jbe

I don't think this is intended, is it?

I don’t know, I’m not familiar with that crate at all. If you feel like this might be not intended, open an issue on their repo

Even if it is intended, it might be insufficiently documented.

[jbe]

I opened the following issue:

bincode::encode_to_vec is incompatible with bincode::serde::encode_to_vec in standard configuration

[steffahn]

Right… it’s almost as if they got their point of which one of skip_fixed_array_length and write_fixed_array_length is supported by bincode::serde::… the wrong way around.