CustomSerializers.md

Customizing ktoml serialization

This page will be useful ONLY for those who plan to customize the serialization and deserialization logic of ktoml.

Custom Deserializer

We suggest to use custom deserializer only for very primitive cases. In case you really need proper custom serializer, you will need to have something like this (this is a real generated code for the serialization):

override fun deserialize(decoder: Decoder): Color {
    val serialDescriptor = descriptor
    var bl = true
    var n = 0
    var l = 0L
    // to read TOML AST properly - you need to run beginStructure first
    val compositeDecoder = decoder.beginStructure(serialDescriptor)
    block4@ while (bl) {
        val n2 = compositeDecoder.decodeElementIndex(serialDescriptor)
        when (n2) {
            // decoding done:
            -1 -> {
                bl = false
                continue@block4
            }
            // element index
            0 -> {
                l = compositeDecoder.decodeLongElement(serialDescriptor, 0)
                n = n or 1
                continue@block4
            }
        }
        throw IllegalArgumentException()
    }
    compositeDecoder.endStructure(serialDescriptor)
    return Color(l)
}

for the following data class:

    @Serializable(with = ColorAsStringSerializer::class)
    data class Color(val rgb: Long)

Simple cases for Deserialization

Imaging you have your class Color:

    @Serializable(with = ColorAsStringSerializer::class)
    data class Color(val rgb: Long)

We have several small workarounds, that would let you override deserializers for your class and using ktoml-native parser and AST:

    object ColorAsStringSerializer : KSerializer<Color> {
        override fun deserialize(decoder: Decoder): Color {
            // please note, that the decoder should match with the real type of a variable:
            // for string in the input - decodeString, for long - decodeLong, etc.
            val string = decoder.decodeString()
            return Color(string.toLong() + 15)
        }
    }

    Toml.decodeFromString<Color>(
        """
            rgb = "0"
        """.trimIndent()
    )