Exhausting when statement with sealed interface and generics

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1

Hello, first post here! I’m having trouble working with sealed classes and generics.

I have a sealed interface with 2 enums that implement it:

sealed interface Nucleotide
enum class DNANucleotide : Nucleotide { Adenine, Cytosine, Guanine, Thymine }
enum class RNANucleotide : Nucleotide { Adenine, Cytosine, Guanine, Uracil }

Then I defined one function for each enum :

fun complement(nucleotide: DNANucleotide): DNANucleotide = when (nucleotide) {
    DNANucleotide.Adenine -> DNANucleotide.Thymine
    DNANucleotide.Cytosine -> DNANucleotide.Guanine
    DNANucleotide.Guanine -> DNANucleotide.Cytosine
    DNANucleotide.Thymine -> DNANucleotide.Adenine
} 
fun complement(nucleotide: RNANucleotide): RNANucleotide = when (nucleotide) {     
    RNANucleotide.Adenine -> RNANucleotide.Uracil 
    RNANucleotide.Cytosine -> RNANucleotide.Guanine 
    RNANucleotide.Guanine -> RNANucleotide.Cytosine 
    RNANucleotide.Uracil -> RNANucleotide.Adenine 
}

At last I want to add a generic function that includes the last two:

fun <N : Nucleotide> complement(nucleotide: N): N = when (nucleotide) {
    is DNANucleotide -> complement(nucleotide)
    is RNANucleotide -> complement(nucleotide)
}

This last function doesn’t compile because the when clause isn’t exhausted and the return type is wrong. Any help or tips to solve this? Thanks!

1 Like
2

It’s probably related to my own ticket I posted a while ago: KT-19645. Right now using exhaustive when on generic type simply seems to be impossible.

1 Like
3

Yes, unfortunately It seems that exhaustive when on generics is not possible for the moment.