Declaring type based JsonConverter

sample.cs

class Program
{
    static void Main(string[] args)
    {
        var r = new RootObj { A = new B { X = "x", Y = "y" } };
        Console.WriteLine(JsonConvert.SerializeObject(r));
    }
}

public class JC<T> : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        throw new NotImplementedException();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        writer.WriteStartObject();
        var contract = (JsonObjectContract)serializer.ContractResolver.ResolveContract(typeof(T));
        foreach(var prop in contract.Properties)
        {
            writer.WritePropertyName(prop.PropertyName);
            serializer.Serialize(writer, prop.ValueProvider.GetValue(value));
        }
        writer.WriteEndObject();
    }
}

public class RootObj
{
    [JsonConverter(typeof(JC<A>))]
    public A A { get; set; }
}

public class A
{
    public string X { get; set; }
}

public class B : A
{
    public string Y { get; set; }
}