ResolveSerializerEventArgs.SetSerializer doesn't allow to set a serializer of a base type.

[aidin36]

Assume the following classes. I handled SerializationContext.ResolveSerializer event, and handler will get called when serializer tries to serialize ChildData. Though DataSerializer can serialize ChildData class, the ResolveSerializerEventArgs.SetSerializer doesn't let me set DataSerializer as the serializer. I have to set a class that explicitly implemented MessagePackSerializer<ChildData>.

This shouldn't be like this, because if I get the serializer with Context.GetSerializer<IData>();, it can handle the ChildData instance correctly. So SetSerializer method should allow me to set that as the ChildData's serializer.

    public class IData
    {
    }

    public class BaseData : IData
    {
        public int DataField { get; set; }
    }

    public class ChildData : BaseData
    {
    }

    public class DataSerializer : MessagePackSerializer<IData>
    {
        public DataSerializer(SerializationContext ownerContext)
            : base(ownerContext)
        {
        }

        protected override void PackToCore(MsgPack.Packer packer, IData objectTree)
        {
            ...
        }

        protected override IData UnpackFromCore(MsgPack.Unpacker unpacker)
        {
            ...
        }
    }

[yfakariya]

Thank you for reporting! I'm checking just to be sure、but do you mean that you get InvalidOperationException when you set to DataSerializer? If so, it is design bug...

[aidin36]

Yes, exactly.

I receive:

InvalidOperationException: The serializer must be MsgPack.Serialization.MessagePackSerializer`1[MsgPackTest.ChildData] type.

Here's a sample implementation of ResolveSerailizer:

static void context_ResolveSerializer(object sender, ResolveSerializerEventArgs e)
{
    if (typeof(IData).IsAssignableFrom(e.TargetType))
    {
        e.SetSerializer<IData>(new BaseDataSerializer(e.Context));
    }
}

[yfakariya]

Sorry for delay. I see, I will fix this.

[yfakariya]

Sorry I forgot about restrictions about generic arguments variance of .NET. I'm thinking solution for it, but it takes more time to fix or it cannot be fixed