[question] System.Text.Json Serialize An Empty interface will get a "{}"

[egmkang]

using System;
using NewtonsoftJson = Newtonsoft.Json.JsonConvert;
using SystemJson = System.Text.Json.JsonSerializer;

public interface Empty { }

public class ObjectA : Empty
{
    public int id { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        Empty a = new ObjectA()
        {
            id = 1,
        };

        Console.WriteLine("System.Text.Json, Serialize<Empty> => {0}", SystemJson.Serialize(a));
        Console.WriteLine("System.Text.Json, Serialize<Object> => {0}", SystemJson.Serialize(a as object));
        Console.WriteLine("Newtonsoft.Json, Serialize<Empty> => {0}", NewtonsoftJson.SerializeObject(a));
        Console.WriteLine("Newtonsoft.Json, Serialize<Object> => {0}", NewtonsoftJson.SerializeObject(a as object));
    }
}

and output is:

System.Text.Json, Serialize<Empty> => {}
System.Text.Json, Serialize<Object> => {"id":1}
Newtonsoft.Json, Serialize<Empty> => {"id":1}
Newtonsoft.Json, Serialize<Object> => {"id":1}

Serialize<Empty> will return {}, is this the correct behavior?

[ghost]

Tagging subscribers to this area: @eiriktsarpalis, @layomia
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Issue Details

---

using System;
using NewtonsoftJson = Newtonsoft.Json.JsonConvert;
using SystemJson = System.Text.Json.JsonSerializer;

public interface Empty { }

public class ObjectA : Empty
{
    public int id { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        Empty a = new ObjectA()
        {
            id = 1,
        };

        Console.WriteLine("System.Text.Json, Serialize<Empty> => {0}", SystemJson.Serialize(a));
        Console.WriteLine("System.Text.Json, Serialize<Object> => {0}", SystemJson.Serialize(a as object));
        Console.WriteLine("Newtonsoft.Json, Serialize<Empty> => {0}", NewtonsoftJson.SerializeObject(a));
        Console.WriteLine("Newtonsoft.Json, Serialize<Object> => {0}", NewtonsoftJson.SerializeObject(a as object));
    }
}

and output is:

System.Text.Json, Serialize<Empty> => {}
System.Text.Json, Serialize<Object> => {"id":1}
Newtonsoft.Json, Serialize<Empty> => {"id":1}
Newtonsoft.Json, Serialize<Object> => {"id":1}

Serialize<Empty> will return {}, is this the correct behavior?

Author:	egmkang
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-

[Joe4evr]

Yes, this is expected at the moment. See #45189.

[eiriktsarpalis]

Support for polymorphic serialization is tracked by #30083. Note that the feature has been cut from .NET 6.

Duplicate of #30083