It would be really great, in a non-theoretical way...

# language-proposals

[mikehearn]

It would be really great, in a non-theoretical way, to have NonEmptySet/NonEmptyMap/NonEmptyList in the Kotlin stdlib. Either as separate classes or using similar type system tricks to MutableList vs List. This would have caught several bugs over the past few months where some code expected a list to contain some elements, iterated over it, but due to a bug the list was empty so the loop body never ran.