reduce

would be great extension for

NonEmptyIterable

https://youtrack.jetbrains.com/issue/KT-21217

Hmm, makes me think if you could combine contracts with some kind of phantom type feature. So you could do something like this:

inline class NonEmptyList<T>(val list: List<T>) {
    contract { list.isNotEmpty() implies list is NonEmptyList }
}

fun someFunction(list: List<T>) {
    if (list.isNotEmpty()) {
        // list is "smart cast" (or conforms) to NonEmptyList.
    }
}

arrow has this out the box: https://arrow-kt.io/docs/arrow/data/nonemptylist/

Not the contract and smart cast stuff 🙂

I see yeah... be interested to see how that offers compile time safety from creating a non empty list, if you passed in a empty list at runtime (e.g from a web service response)

The same compile time safety you would get by passing null to a non-null parameter at runtime. 😉

oh, ok