commonMain.dk.cachet.carp.common.infrastructure.serialization.PolymorphicEnumSerializer.kt Maven / Gradle / Ivy

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package dk.cachet.carp.common.infrastructure.serialization

import kotlinx.serialization.ExperimentalSerializationApi
import kotlinx.serialization.KSerializer
import kotlinx.serialization.descriptors.SerialDescriptor
import kotlinx.serialization.descriptors.buildClassSerialDescriptor
import kotlinx.serialization.encoding.Decoder
import kotlinx.serialization.encoding.Encoder
import kotlinx.serialization.encoding.decodeStructure
import kotlinx.serialization.encoding.encodeStructure


/**
 * A serializer which supports registering [Enum]s as subclasses in polymorphic serialization when class discriminators are used.
 * When class discriminators are used, an enum is not encoded as a structure which the class discriminator can be added to.
 * An exception is thrown when initializing [Json]: "Serializer for  of kind ENUM cannot be serialized polymorphically with class discriminator."
 * This serializer encodes the enum as a structure with a single `value` holding the enum value.
 *
 * Use this serializer to register the enum in the serializers module, e.g.:
 * `subclass( ::class, PolymorphicEnumSerializer( .serializer() )`
 */
@OptIn( ExperimentalSerializationApi::class )
class PolymorphicEnumSerializer>( private val enumSerializer: KSerializer ) : KSerializer
{
    override val descriptor: SerialDescriptor = buildClassSerialDescriptor( enumSerializer.descriptor.serialName )
    {
        element( "value", enumSerializer.descriptor )
    }

    override fun deserialize( decoder: Decoder ): T =
        decoder.decodeStructure( descriptor )
        {
            decodeElementIndex( descriptor )
            return decodeSerializableElement( descriptor, 0, enumSerializer )
        }

    override fun serialize( encoder: Encoder, value: T ) =
        encoder.encodeStructure( descriptor )
        {
            encodeSerializableElement( descriptor, 0, enumSerializer, value )
        }
}