[API Proposal]: Add Order property to KnownTypeAttribute

[weitzhandler]

Background and motivation

In some serialization systems (e.g. protobuf), any member, including those of derived types require a unique order indicator.

It would thus be beneficial to include the Order property in the KnownType attribute as well, so the serializer knows how to order to items of the derived types.

API Proposal

 public sealed class KnownTypeAttribute : Attribute
 {
     public string? MethodName { get; }
     public Type? Type { get; }
+    public int Order { get; set; }
 }

API Usage

[DataContract]
[KnownType(typeof(Dog), Order = 100)]
public class Animal
{
    [DataMember(Order = 1)]
    public string Name { get; set; }
}

[DataContract]
public class Dog
{
    [DataMember(Order = 1)]
    public int TailLength { get; set; }
}

Alternative Designs

No response

Risks

No response