A modern programming language that makes developers happier.

kotlinlang

See limitations part
<https://github.com/Kotlin/KEEP/blob/master/proposals/stdlib/result.md>

&gt;  The rationale behind these limitations is that future versions of Kotlin may expand and/or change semantics of functions that return `Result` type and null-safety operators may change their semantics when used on values of `Result` type. In order to avoid breaking existing code in the future releases of Kotlin and leave door open for those changes, the corresponding uses produce an error now. Exceptions to this rule are made for carefully-reviewed declarations in the standard library that are part of the `Result` type API itself.

ok i see. it's not much of a use no me if i cannot use it in a public api

Checkout 'Either' in Arrow-kt or create your own version for explicit error handling. 

This one also I think is a simpler alternative to `Either`, and has similar API to `kotlin.Result`, I've been using it and it served me well.
<https://github.com/npryce/result4k>

you can use `kotlin.Result` if you specify
```-Xallow-result-return-type```
in compiler args. It's experimental though and the way it works and its API could change before it completes its experimental stage, that's why it isn't enabled by default.

`Either` in Arrow (becoming BIO in 0.11 release) is a good place to start if you want to really get into FP. If you just want the Result type, then result4k looks like a very good option. Or opting into experimental.