Either introduce getOrElseThrow method

[mipo256]

I have not found any appropriate issue, so I'm leaving it here.

So, assume we have the following function that returns the karrow Either:

fun <T> send(body: T) : Either<ExternalFailure, ExternalSuccess> {
    // implementation
}

What it does is it sends over a specific protocol some information, it does not matter for this issue. What I need is to call the function send(body: t), and I need to throw a RuntimeException to the callee, in case we hit an error. This is the contract that I have to adhere to.

The way I should recognize that the error had happened is by checking if the Either is Left. So I need something like this:

return send(myBody).throwOnLeft({ left ->
    ProtocolIOException("Something bad had happened :${left}")
})

I do not need to mapLeft, or getOrElse or anything - I just need to return the ExternalSuccess (the Right in my case), or I need to throw an exception.

Is there any built-in way to do so?

[mipo256]

I can provide a PR if needed. We have implemented this function as an extension to karrow Either

[kyay10]

That's just:

return send(myBody).getOrElse { left ->
    throw ProtocolIOException("Something bad had happened :${left}")
}

[mipo256]

Yes, that can be done this way, I know, but this function is in general meant to compute the default value in case we have Left. The lambda that is passed is of type (A) -> B, where the return type is B.

You are correct @kyay10, but my point is that it may be a good idea to have a dedicated method for it? I'm not insisting, just sharing my thoughts that calling getOrElse was not obvious from the first glance to solve the problem

[kyay10]

Part of the intention of having such a type is that you can pass in an (A) -> Nothing function, e.g. one that throws an exception. I think this is a wider Kotlin trend that we shouldn't deviate too hard from (for instance, nullableFoo ?: error("foo is null") is idiomatic Kotlin, and similarly send(myBody).getOrElse { error("response was $it") })

[mipo256]

@kyay10 So, should I try to submit the PR and we'll see how it goes?

[mipo256]

ping here @kyay10 :)

[serras]

I agree here with @kyay10, the idiomatic way to handle this in Kotlin is writing getOrElse { throw ... }, and we would like to keep the API as close as possible to these idioms.