Kotlin toJson Extensions

toJson.kt

private fun convertToJson(v: Any?): String {
    return when (v) {
        is String -> v.toJson()
        is Boolean -> v.toJson()
        is Number -> v.toJson()
        is Array<*> -> v.toJson()
        is Collection<*> -> v.toJson()
        is Map<*, *> -> v.toJson()
        else -> v?.toJson() ?: "null"
    }
}

fun String.toJson(): String = "\"${this.replace("\"", "\\\"")}\""
fun Boolean.toJson(): String = if (this) "true" else "false"
fun Number.toJson(): String = this.toString()

fun Array<*>.toJson(): String = "[${this.joinToString(",") { convertToJson(it) }}]"
fun Collection<*>.toJson(): String = "[${this.joinToString(",") { convertToJson(it) }}]"

fun Map<*, *>.toJson(): String {
    return "{${
        this.entries.joinToString(",") {
            "\"${
                if (it.key is String || it.key is Boolean || it.key is Number) it.key!!.toJson()
                else "__not_a_primitive__"
            }\":${convertToJson(it.value)}"
        }
    }}"
}

fun Any.toJson(): String {
    return if (!this::class.isData)
        "{\"__not_a_data_class__\":\"${this::class.qualifiedName}\"}"
    else "{${
        this.javaClass.declaredFields.joinToString(",") {
            it.isAccessible = true
            "\"${it.name}\":${convertToJson(it.get(this))}"
        }
    }}"
}

TODO: Throw on circular references (or max. depth)