Kotlin - assign value of enum to variable without .value

Question

What it's like now:

class Trial {
    companion object{
        @JvmStatic fun main(args: Array<String>){
            val message = Message.ALREADY_REGISTERED.value
            println(message);
        }
    }
}

enum class Message constructor(val value: String){
    ALREADY_REGISTERED("You've already been registered")
}

This outputs: You've already been registered. But I was wondering, is there a way to just assign val message = Message.ALREADY_REGISTERED and have the value immediately without having to use .value?

When trying this (with the code I want)

class Trial {
    companion object{
        @JvmStatic fun main(args: Array<String>){
            val message = Message.ALREADY_REGISTERED
            println(message);
        }
    }
}

enum class Message constructor(val value: String){
    ALREADY_REGISTERED("You've already been registered")
}

it outputs ALREADY_REGISTERED.

So can I make the value of the enum return default instead of it's name?

The question looks like you are asking for an implicit type conversion Message -> String, while you are probably not. — voddan
– voddan, Commented Jan 12, 2017 at 17:15
Well that would be a workaround but quite possibly could work — Ivafo
– Ivafo, Commented Jan 12, 2017 at 17:26

mfulton26 · Accepted Answer · 2017-01-12 14:38:45Z

8

You need to override toString() for your enum class:

enum class Message(val value: String) {
    ALREADY_REGISTERED("You've already been registered");

    override fun toString() = value
}

You can also use class delegation if you want to be able to treat your enum class as a CharSequence (like StringBuilder and other String-like classes):

enum class Message(val value: String) : CharSequence by value {
    ALREADY_REGISTERED("You've already been registered");

    override fun toString() = value
}

Then you can use it just like any other CharSequence. e.g.:

buildString {
    append("Message received: ")
    appendln(Message.ALREADY_REGISTERED)
    appendln()
    appendln("Don't forget to do your laundry.")
}

edited Jan 12, 2017 at 14:38

answered Jan 12, 2017 at 14:06

mfulton26

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6 Comments

Ivafo Over a year ago

thanks, just wondering: why is the semicolon required? Because compiler will think that I'm trying to declare another enum?

mfulton26 Over a year ago

Correct, see Anonymous Classes - Enum Classes - Kotlin Programming Language for details. See also the grammar for enum classes.

Ivafo Over a year ago

This only seems to work when using println, if message is changed to val message: String = Message.ALREADY_REGISTERED the same problem is still present

mfulton26 Over a year ago

I've updated my answer. You cannot extend String but you can get close. Java/Kotlin does this in lots of places with the CharSequence interface which String implements. In fact, when ever you define methods that receive a String and you do not require that input String to be immutable then you should use CharSequence instead for this exact purpose (e.g. take a look at the various methods in the kotlin.text package).

Ivafo Over a year ago

Hmm then the .value will be easier haha. Thanks for your help!

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