Unstable output from kotlinx.serialization

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1

Hello,

This code Kotlin Playground: Edit, Run, Share Kotlin Code Online tests the kotlinx.serialization

Mostly, the output is:

{"name":"Alice","age":30,"swtK":false,"now3":1741025383879}
{"name":"David","age":32,"now3":1741025383922}
User(name=Alice, age=30, swtK=false)
User(name=David, age=32, swtK=true)

Very rarely, the output is like shown in the screenshot.

{"name":"Alice","age":30,"swtK":false,"now3":1740944237946,"now4":1740944237,"now5":1740944237}
{"name":"David","age":32,"now3":1740944237996,"now4":1740944237,"now5":1740944237}
User(name=Alice, age=30, swtK=false)
User(name-David, age=32, swtK=true)

  1. Why are the properties now4 and now5 not encoded (encodeToString)?

  2. Why are the boolean properties (swtK) not decoded (decodeFromString) when the value is TRUE?

  3. How to use/import io.realm.kotlin.* to test it?

  4. What is your recommendation to save the creation timestamp (second or millisecond from 1.1.1970) of a new record?

Thanks

import kotlinx.serialization.Serializable
import kotlinx.serialization.SerialName
import kotlinx.serialization.json.Json
import kotlinx.serialization.encodeToString
import kotlinx.serialization.decodeFromString
import java.time.Instant
import java.util.Calendar
import java.util.Date
//import io.realm.kotlin.ext.query
//import io.realm.kotlin.serializers.RealmInstantKSerializer
//import io.realm.kotlin.types.RealmInstant
//import io.realm.kotlin.types.RealmObject
//import io.realm.kotlin.types.annotations.PrimaryKey

@Serializable
data class User(var name:String, var age:Int, var swtK:Boolean=true){
 //@Transient
 //@PrimaryKey
 //var idPK:ObjectId=ObjectId()
 //@Serializable(RealmInstantKSerializer::class)
 //var nowK:RealmInstant=RealmInstant.now()
 //var now2:Long=RealmInstant.now().toInstant().epochSecond
 var now3:Long=Calendar.getInstance().timeInMillis
 var now4:Long=Instant.now().epochSecond
 var now5:Long=Date().toInstant().epochSecond
 constructor():this(name="", age=0, swtK=true)
 companion object
}

fun main() {
 var line=""
 lateinit var user:User
 val alice=User("Alice", 30, false)
 val david=User("David", 32, true)
 val listU:List<User> =listOf(alice, david)
 val convStr=mutableListOf<String>()
 listU.forEach {item ->
  line=Json.encodeToString(item)
  convStr.add(line)
  println(line)
 }
 convStr.forEach {item ->
  user=Json.decodeFromString<User>(item)
  println(user)
 }
}

FzCUC
FzCUC1971×1369 259 KB

2

delay seems to be somewhat consistent?

import kotlinx.serialization.Serializable
import kotlinx.serialization.SerialName
import kotlinx.serialization.json.Json
import kotlinx.serialization.encodeToString
import kotlinx.serialization.decodeFromString
import java.time.Instant
import java.util.Calendar
import java.util.Date

@Serializable
data class User(var name:String, var age:Int, var swtK:Boolean=true){
 var now3:Long=Calendar.getInstance().timeInMillis
 var now4:Long=Instant.now().epochSecond
 var now5:Long=Date().toInstant().epochSecond
 constructor():this(name="", age=0, swtK=true)
 companion object
}

suspend fun main() {
 var line=""
 lateinit var user:User
 val alice=User("Alice", 30, false)
 val david=User("David", 32, true)
 val listU:List<User> =listOf(alice, david)
 val convStr=mutableListOf<String>()
 kotlinx.coroutines.delay(1000)
 listU.forEach {item ->
  line=Json.encodeToString(item)
  convStr.add(line)
  println(line)
 }
 convStr.forEach {item ->
  user=Json.decodeFromString<User>(item)
  println(user)
 }
}

Seems like an issue where kotlinx serialization compares the value of now4 and now5 to the “default” value.
Using @EncodeDefault seems to fix this:

import kotlinx.serialization.Serializable
import kotlinx.serialization.SerialName
import kotlinx.serialization.json.Json
import kotlinx.serialization.encodeToString
import kotlinx.serialization.decodeFromString
import kotlinx.serialization.EncodeDefault
import java.time.Instant
import java.util.Calendar
import java.util.Date

@Serializable
data class User(var name:String, var age:Int, var swtK:Boolean=true){
 var now3:Long=Calendar.getInstance().timeInMillis
 @EncodeDefault
 var now4:Long=Instant.now().epochSecond
 @EncodeDefault
 var now5:Long=Date().toInstant().epochSecond
 constructor():this(name="", age=0, swtK=true)
 companion object
}

suspend fun main() {
 var line=""
 lateinit var user:User
 val alice=User("Alice", 30, false)
 val david=User("David", 32, true)
 val listU:List<User> =listOf(alice, david)
 val convStr=mutableListOf<String>()
 listU.forEach {item ->
  line=Json.encodeToString(item)
  convStr.add(line)
  println(line)
 }
 convStr.forEach {item ->
  user=Json.decodeFromString<User>(item)
  println(user)
 }
}