Multiple constructors are not available on Android; default constructor is lost!

[pronebird]

#[uniffi::export(async_runtime = "tokio")]
impl NymEnvironment {
    #[uniffi::constructor]
    pub async fn new(
        cache_dir: PathBuf,
        network_name: &str,
    ) -> Result<Self, VpnError> {
        todo!()
    }

    #[uniffi::constructor]
    pub fn new_with_mainnet_fallback() -> Result<Self, VpnError> {
        todo!()
    }

    pub async fn __stub_to_keep_compiler_happy(&self) {
        // todo: remove after updating to uniffi 0.31
    }
}

When trying to create object using new initializer, I get nasty argument mismatch issue.

val env = NymEnvironment(storagePath, "some")

The default initailizer looks like some internal uniffi method that must not be exposed:

constructor(withHandle: UniffiWithHandle, handle: Long) {

[bendk]

I don't think this is an issue with multiple constructors, it's that the constructor is async which isn't supported on Kotlin.

I also think you might have issues with that PathBuf argument. UniFFI doesn't support that directly I usually just use String to pass paths across the FFI. Maybe the only reason you're not seeing those yet is because we're not generating the constructor yet.

[pronebird]

I also think you might have issues with that PathBuf argument. UniFFI doesn't support that directly I usually just use String to pass paths across the FFI. Maybe the only reason you're not seeing those yet is because we're not generating the constructor yet.

I have custom type implemented. We use UTF-8 in Kotlin/Swift so that should work just fine.

uniffi::custom_type!(PathBuf, String, {
    remote,
    try_lift: |val| Ok(PathBuf::from(val)),
    lower: |val| val.display().to_string()
});

[pronebird]

I don't think this is an issue with multiple constructors, it's that the constructor is async which isn't supported on Kotlin.

This does not seem to be correct. It works fine as long as the method is not called new but something like newSomething, then it appears in the output.

[bendk]

I don't think this is an issue with multiple constructors, it's that the constructor is async which isn't supported on Kotlin.

This does not seem to be correct. It works fine as long as the method is not called new but something like newSomething, then it appears in the output.

That's the difference between what UniFFI calls a primary constructor vs an alternate constructor. In Kotlin, UniFFI generates:

• A primary constructor that has the withHandle argument. This is an implementation detail and doesn't correlate to any user-defined constructor.
• A secondary constructor for the new function that calls the primary constructor. I don't believe this can be async by Kotlin's rules.
• A companion class method for all alternate constructors. These can be async.

There's a logic to it all, but I'm sure it could be improved. Maybe async constructors should always be considered alternate constructors?

[pronebird]

Yeah I think so, they shouldn't just disappear.

[bendk]

Yes, disappearing is the worst option. Another idea would be to throw an error and tell the user to name the constructor something other than new. It feels a bit weird to me this is the only case where we're generating a companion method named new and it may lead to user confusion.

I'm not sure if that's best though, what's your opinion?

[pronebird]

@bendk throwing some error during build time would be the best option here. At least it wouldn't go unnoticed.

[bendk]

Just put up a PR for this that defines the constructor, but makes it throw. I'm not sure if that's the best option or not, let's discuss in the PR.