How do I store instances of an `enum class` implementing an

Question

How do I store instances of an `enum class` implementing an interface in a `TreeMap` such a way that I can set get set them without throwing a `ClassCastException` So far I have ```interface MyEnumInterface enum class MyEnumClass MyEnumInterface ``` `var myTreeMap TreeMap lt MyEnumInterface gt Unit gt = TreeMap ` however when I call this method passing an instance of `MyEnumClass` ```fun add howToExecute gt Unit myEnum MyEnumInterface myTreeMap myEnum = howToExecute ClassCastException here ``` I get a `ClassCastException` Why does this happen Why doesn t it happen when the instance is passed to the add method What s the most appropriate resolution please

Andrew Ebling · Answer

Is this happening because the compiler is only generating code specific to the interface Can I add some kind of type constraint to the method signature to say something which implements MyEnumInterface

diesieben07 · Answer

I can t reproduce this with the code you ve shared <https pl kotl in 7c jbm5dL> Can you provide more details

diesieben07 · Answer

One thing that I can imagine happening is that if you use an implementation of `MyEnumInterface` that is not also implementing `Comparable` which enums do by default `TreeMap` requires either the keys to implement `Comparable` or otherwise be given an external `Comparator`

Andrew Ebling · Answer

yes that s exactly what I m doing < diesieben07> and I m at a loss to explain why it works in the playground but not in my production code

Andrew Ebling · Answer

this is in an Android app could that make any difference

diesieben07 · Answer

I am not too familiar with Android Can you share what line exactly throws the ClassCastException as well as the message Does it happen inside `TreeMap` code

Andrew Ebling · Answer

```at java lang Enum compareTo Enum java 186 at java lang Enum compareTo Enum java 61 at java util TreeMap put TreeMap java 569 at com mycompany MyObject add MyObject kt 42 ```

diesieben07 · Answer

So you must have more than one entry in the map Is it all the same `enum`

diesieben07 · Answer

Because if not obviously they cannot be ordered within each other

Andrew Ebling · Answer

ah that will be it

diesieben07 · Answer

then you must provide an external `Comparator` that knows how to compare all possible keys

Andrew Ebling · Answer

many thanks for your help clap

kqr · Answer

< diesieben07> nice