Protobuf-Net error message: No Serializer defined for type: System.Type

Question

I am getting the following error message when trying to serialize List<Tuple<string, Type, object>>: No Serializer defined for type: System.Type

I tried both, just serializing the above collection or serializing a class that has the same collection defined as protoMember. Both result in the same error message.

Is this a non-supported type? I assume it is supported and I overlooked something else but maybe I am incorrect?

Thanks for any pointers that may help resolve this...

Answer 1

Edit:

Support for Type serialization is included in r580

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protobuf-net is intended to serialize your data, not your implementation; Type is an implementation detail. Strictly speaking, it wouldn't be hugely hard to add (some of the implementation-specific details already essentially end up storing Type info, via the assembly-qualified-name), but: it isn't a key scenario, and in many ways is not something I would encourage you to serialize - the whole point of protocol buffers is that you can load the data on any platform, with version tolerance a key feature. Storing Type information violates both of these.

It should also be noted that most other serializers (except perhaps BinaryFormatter, which already breaks every rule of platform/version-tolerance) will also refuse to serialize a Type; XmlSerializer, DataContractSerializer, JavaScriptSerializer etc all throw an exception for this scenario (I just checked them).

Additionally: object is even less supportable, unless you use the DynamicType feature.

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Here's how it could be done via a surrogate on Type:

using ProtoBuf;
using ProtoBuf.Meta;
using System;
using System.Runtime.Serialization;

static class Program
{
    public static void Main(string[] args)
    {
        // register a surrogate for Type
        RuntimeTypeModel.Default.Add(typeof(Type), false)
                                .SetSurrogate(typeof(TypeSurrogate));
        // test it
        var clone = Serializer.DeepClone(new Foo { Type = typeof(string) });
    }
}

[ProtoContract]
class TypeSurrogate
{
    [ProtoMember(1)]
    public string AssemblyQualifiedName { get; set; }
    // protobuf-net wants an implicit or explicit operator between the types
    public static implicit operator Type(TypeSurrogate value)
    {
        return value==null ? null : Type.GetType(value.AssemblyQualifiedName);
    }
    public static implicit operator TypeSurrogate(Type value)
    {
        return value == null ? null : new TypeSurrogate {
            AssemblyQualifiedName  = value.AssemblyQualifiedName };
    }
}

[DataContract]
public class Foo
{
    [DataMember(Order=1)]
    public Type Type { get; set; }
}