kovenant | Promises for Kotlin | Reactive Programming library

Turns out it's Funktionale being a bit of a bad citizen that's causing the problem. Using class lookup (Ctrl + N on Windows) for the given class, I got two results. One of them inside the expected JetBrains annotation package, the other inside Funktionale's.

Looking at the contents of this package, you can see that it actually contains a whole bunch of externally defined annotations inside it:

I can't say why they did this instead of having these libraries declared as dependencies though.

Now, for a list of possible solutions.

1. Open up the .jar file provided by the dependency, remove the offending packages from it, repack it, and include it in your project as a local .jar file.

2. Look into hacky solutions that try to remove .class files from a Gradle dependency. I found this while looking into this, but it didn't seem to work for me.

3. Raise an issue with the library authors on GitHub and wait for a response and a new release.

4. Fork and re-publish the library with the offending packages removed.

5. Use Arrow instead. This is a new functional Kotlin library created by the maintainers of Funktionale and Kategory together. They talk about it on the a Talking Kotlin podcast episode here. Unfortunately, I don't have personal experience with either of these libraries, but it might suit your needs.

There's an issue with retrofit-vertx you are using. OkHttp3's ResponseBuilder requires message to be not null, but VertxCallFactory doesn't set it.

It's fixed in the latest version, but as it's still in development, you have to use snapshot:

Some of the base definitions do not have generic bounds for E but almost all of the extension functions do indicate the E is of type Exception. Viewing the source code in Kovenant promises-api.kt shows that it is clear that most things have this expectation.

You can simply change your error class to be a descendant of Exception:

You get Promise, Exception> type when you return another promise from the lambda passed to then. Therefore in the next then the argument it has type Promise instead of Int.

In order to flatten promise you can use unwrap function, which converts Promise> into Promise. Then your example would look like: