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I need some help with deserialization. I get an `I...
# serialization
k
I need some help with deserialization. I get an 
IndexOutOfBoundsException
and I do not really get why. (thread)
I have JSON of the following form:
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{
  "headerFields": [
    {
      "key": "key1",
      "label": "label1",
      "value": "value1"
    },
    {
      "key": "key2",
      "label": "label2",
      "value": "42",
      "format": "scientific"
    },
    {
      "key": "key2",
      "label": "label2",
      "value": "value2",
      "date": "<timestamp>"
    }
  ]
}
I tried to parse it with the following class but it fails with the exception below:
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@Serializable       // Line (2)
data class Fields(
    val headerFields: List<FieldKeys> = emptyList(),
)

@Serializable(with = FieldKeysDeserializer::class)
sealed interface FieldKeys

@JvmInline          // Line (1)
@Serializable
value class StandardKeys(val value: StandardFieldKeys) : FieldKeys

@JvmInline
@Serializable
value class DateKeys(val value: DateFieldKeys) : FieldKeys

@JvmInline
@Serializable
value class NumberKeys(val value: NumberFieldKeys) : FieldKeys

object FieldKeysDeserializer : JsonContentPolymorphicSerializer<FieldKeys>(FieldKeys::class) {
    override fun selectDeserializer(element: JsonElement): DeserializationStrategy<out FieldKeys> {
        if (element !is JsonObject) throw RuntimeException("failed to decode fields dict")
        return when {
            "date" in element.jsonObject -> DateKeys.serializer()
            "format" in element.jsonObject -> NumberKeys.serializer()
            else -> StandardKeys.serializer()
        }
    }
}

@Serializable
data class StandardFieldKeys(
    val key: String,
    val value: String,
    val label: String? = null,
)

@Serializable
data class DateFieldKeys(
    val key: String,
    val value: String,
    val label: String? = null,
    val date: String,
)

@Serializable
data class NumberFieldKeys(
    val key: String,
    val value: Integer,
    val format: String,
    val label: String? = null,
)
The exception that I get is this one:
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console
Index -1 out of bounds for length 0
java.lang.IndexOutOfBoundsException: Index -1 out of bounds for length 0
    at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64)
    at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70)
    at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:248)
    at java.base/java.util.Objects.checkIndex(Objects.java:372)
    at java.base/java.util.ArrayList.remove(ArrayList.java:536)
    at kotlinx.serialization.internal.TaggedDecoder.popTag(Tagged.kt:321)
    at kotlinx.serialization.internal.TaggedDecoder.decodeInline(Tagged.kt:212)
    at StandardKeys$$serializer.deserialize-2umswgo(FieldKeys.kt:(1))
    at StandardKeys$$serializer.deserialize(FieldKeys.kt:(1))
    at kotlinx.serialization.json.internal.PolymorphicKt.decodeSerializableValuePolymorphic(Polymorphic.kt:59)
    at kotlinx.serialization.json.internal.AbstractJsonTreeDecoder.decodeSerializableValue(TreeJsonDecoder.kt:51)
    at kotlinx.serialization.json.internal.TreeJsonDecoderKt.readJson(TreeJsonDecoder.kt:24)
    at kotlinx.serialization.json.Json.decodeFromJsonElement(Json.kt:119)
    at kotlinx.serialization.json.JsonContentPolymorphicSerializer.deserialize(JsonContentPolymorphicSerializer.kt:93)
    at kotlinx.serialization.json.internal.PolymorphicKt.decodeSerializableValuePolymorphic(Polymorphic.kt:59)
    at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableValue(StreamingJsonDecoder.kt:38)
    at kotlinx.serialization.encoding.AbstractDecoder.decodeSerializableValue(AbstractDecoder.kt:43)
    at kotlinx.serialization.encoding.AbstractDecoder.decodeSerializableElement(AbstractDecoder.kt:70)
    at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableElement(StreamingJsonDecoder.kt:111)
    at kotlinx.serialization.encoding.CompositeDecoder$DefaultImpls.decodeSerializableElement$default(Decoding.kt:537)
    at kotlinx.serialization.internal.CollectionLikeSerializer.readElement(CollectionSerializers.kt:80)
    at kotlinx.serialization.internal.AbstractCollectionSerializer.readElement$default(CollectionSerializers.kt:51)
    at kotlinx.serialization.internal.AbstractCollectionSerializer.merge(CollectionSerializers.kt:36)
    at kotlinx.serialization.internal.AbstractCollectionSerializer.deserialize(CollectionSerializers.kt:43)
    at kotlinx.serialization.json.internal.PolymorphicKt.decodeSerializableValuePolymorphic(Polymorphic.kt:59)
    at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableValue(StreamingJsonDecoder.kt:38)
    at kotlinx.serialization.encoding.AbstractDecoder.decodeSerializableValue(AbstractDecoder.kt:43)
    at kotlinx.serialization.encoding.AbstractDecoder.decodeSerializableElement(AbstractDecoder.kt:70)
    at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableElement(StreamingJsonDecoder.kt:111)
    at Fields$$serializer.deserialize(PassStructureDict.kt:(2))
    at Fields$$serializer.deserialize(PassStructureDict.kt:(2))
    at kotlinx.serialization.json.internal.PolymorphicKt.decodeSerializableValuePolymorphic(Polymorphic.kt:59)
    at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableValue(StreamingJsonDecoder.kt:38)
    at kotlinx.serialization.json.Json.decodeFromString(Json.kt:100)
    at FieldsTest.deserializes Fields(FieldKeysTest.kt:<call side>)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
    at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
    at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.runTestClass(JUnitTestClassExecutor.java:110)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:58)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:38)
    at org.gradle.api.internal.tasks.testing.junit.AbstractJUnitTestClassProcessor.processTestClass(AbstractJUnitTestClassProcessor.java:62)
    at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:51)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
    at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
    at com.sun.proxy.$Proxy2.processTestClass(Unknown Source)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker$2.run(TestWorker.java:176)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)
    at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)
    at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:133)
    at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:71)
    at worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
    at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)
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