I'm trying to map enum to int values: ```@Serializ...

# serialization

[Philip Dukhov]

I'm trying to map enum to int values:

@Serializable
enum class ItemType {
    @SerialName("0") Zero,
    @SerialName("1") First,
}

But it fails with the following exception:

JsonDecodingException: Unexpected JSON token at offset 194: Expected quotation mark '"', but had '1' instead
    JSON input: ....."type":1,.....

It doesn't seem to work because SerialName is expecting a string and json has an int.

I can think of two ways to solve this:
1. Enabling lenient mode - I don't like this solution as it also removes restrictions from other fields, which I prefer to keep
2. Implementing a custom serializer - seems like too much of boilerplate code for such a simple task

Am I missing something?

[Adam S]

hi, I think those are your two options. and I think a custom serializer is the best one. It wouldn't be very much boilerplate, see Json transformations. Do you have some example JSON?

[Adam S]

here's a demo that serializes ItemType to/from an integer. It uses requireNotNull(...) to verify the ItemType is known. And personally I prefer hardcoding the ID of an enum, rather than relying on .ordinal - but you can do that too.

If you wanted to do this for lots of enums, that's possible too. You'd have to make your own annotation and mark it as @SerialInfo. Then write a single 'enum-as-int serializer', which would be used for all required enums.

Untitled.cpp

[Philip Dukhov]

@Adam S Thanks, the custom annotation option seems interesting to me, I haven't used SerialInfo before, could you give me a link to an example or documentation? I have not been able to find it on my own.

[Adam S]

yes there's not much documentation for it. There's some info in Dokka https://kotlin.github.io/kotlinx.serialization/kotlinx-serialization-core/kotlinx.serialization/-serial-info/index.html

[Adam S]

I can't really think of a good way to get @SerialInfo to work actually. It gets a bit messy because the point of it is that the KXS plugin will generate a SerialDescriptor that includes the @SerialInfo annotation, but in this instance you'd need to write your own descriptor anyway...

[Adam S]

probably the cleanest way to re-use an 'enum as int' serializer is to use an interface, like this.

demo2_kt.cpp

[Philip Dukhov]

@Adam S Thank you, that seems like the cleanest solution to me so far