Multi-Value Return in Wasmer

[vasigorc]

Hello,

I am trying to reproduce this Wasmtime example using Wasmer to show a simple case of returning tuples from a WASM function.

Here is my TOML:

[package]
name = "hello-mvr"
version = "0.1.0"
edition = "2024"

[dependencies]
wasmer = "5.0.6"

, and the used .wat file:

(module
  (func $swap (import "" "swap") (param i32 i32) (result i32 i32))

  (func $myfunc (export "myfunc") (param i32 i32) (result i32 i32)
    (call $swap (local.get 0) (local.get 1))
  )
)

, and the actual code:

// src/main.rs
use std::error::Error;

use wasmer::*;

fn main() -> Result<(), Box<dyn Error>> {
    let mut store = Store::default();
    let module = Module::from_file(&store, "mvr.wat")?;

    let callback_func = Function::new_typed(&mut store, |a: i32, b: i32| -> (i32, i32) { (b, a) });

    let import_object = imports! {
        "" => {
            "swap" => callback_func,
        }
    };

    let instance = Instance::new(&mut store, &module, &import_object)?;

    let myfunc = instance
        .exports
        .get_typed_function::<(i32, i32), (i32, i32)>(&mut store, "myfunc")?;
    let (a, b) = myfunc.call(&mut store, 13, 43)?;
    println!("Swapping {} and {} produces {} and {}.", 13, 43, a, b);

    Ok(())
}

Unfortunately when I build and run, I get this:

cargo run --release  
    Finished `release` profile [optimized] target(s) in 0.06s
     Running `target/release/hello-mvr`
Swapping 13 and 43 produces 43 and 1634740384.

whereas, the aforementioned Wasmtime example correctly prints "Swapping 13 43 produces 43 13".

What am I doing wrong?

[vasigorc]

I did find an example similar in purpose using Wasmer here: https://github.com/wasmerio/wasmer/blob/main/examples/features.rs#L56 But syntax-wise it looks less concise as the Wasmtime one - I will attribute it to my lack of knowledge.