How can I declare an argument in Kotlin that accepts (only) enums

Question

For example: I want to declare an exception:

class UnexpectedEnumException(enum: Enum...) : Exception("Unexpected enum $enum")

In Java I can do this by

public class UnexpectedEnumException extends RuntimeException {

    public UnexpectedEnumException(Enum<?> en) {
        super("Unexpected enum " +  en);
    }

You can also make the class generic based on the enum as well if you wanted: `class UnexpectedEnumException>(enum: T)` — Ruckus T-Boom, Oct 16 '17 at 15:51

score 4 · Answer 1 · answered Oct 15 '17 at 11:52

To expand on JB Nizet's comment, which should have been an answer, generics in Kotlin are a little bit different from Java. The usage of the star is explained in the Star projections section of documentation.

class UnexpectedEnumException(enum: Enum<*>)
    : Exception("Unexpected enum $enum")

How can I declare an argument in Kotlin that accepts (only) enums

1 Answers1