Discriminator for class hierarchies

[jnm2]

If a type is virtual, the possibility exists that you might need to serialize a piece of information to identify which concrete class to use. Derived or implementing classes may have the same set of properties but signify different things as in a discriminated union, so an additional property should probably be synthesized to identify the correct concrete type.

A "$type"-style property is dangerous and not very pretty. With JSON.NET I usually have a JsonConverter that looks like this (very old implementation):

JsonSerializerSettings.Converters.Add(
    new DerivedDiscriminatorConverter<SomeBaseType>("type")
        .Map<ConcreteType1>("1")
        .Map<ConcreteType2>("2"));

It adds the property "type": "1" for ConcreteType1 and "type": "2" for ConcreteType2. Names are usually more interesting and enum-like. This way known (and vetted!) concrete implementations will roundtrip correctly in an object graph.

I wonder if something similar would make sense for Gu.Xml, maybe even built in?

[JohanLarsson]

<?xml version="1.0" encoding="utf-16"?>
<WithTwoPublicMutableBoxedProperties xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Value1 xsi:type="xsd:int">1</Value1>
  <Value2 xsi:type="xsd:double">2</Value2>
</WithTwoPublicMutableBoxedProperties>

XmlSerializer does ^

[jnm2]

What about types that don't map to XSD primitives?