Keep an Eye on TypeInfo Serialization

[AdamsLair]

Making the Duality Core a PCL also requires switching from the old Type API to the new TypeInfo API. Unfortunately, Serialization will have a hard time coping with this, to the point that I would consider TypeInfo completely unsupported as a serializable type.

• The .Net Framework makes TypeInfo derive from Type in .Net 4.5, but Windows Store apps have Type derive from object, and TypeInfo directly from MemberInfo.
• At runtime in .Net 4.5, these are RuntimeType objects, which derive from TypeInfo, which derives from Type. Thus, the two classes are completely indistinguishable when serializing them, because RuntimeType is simply both of them.
• When deserializing, a decision needs to be made which kind of object to retrieve - TypeInfo or Type. This choice is purely virtual in .Net 4.5, but distinctive in Windows Store apps. Choosing the wrong one will result in an error when attempting to assign the value to a field or array index.

This results in an erroneous deserialization of content, depending on whether the underlying platform implements Type as part of the TypeInfo inheritance or not. There is nothing Duality can do about this, because there is no difference between the two for an object in the .Net 4.5 runtime.

[AdamsLair]

Until further notice, TypeInfo should be regarded as completely unsupported in serialization. Use Type for serializable fields instead.

[AdamsLair]

Created a StackOverflow Question for gathering some feedback on the matter and seeing if there is something I'm missing.

[AdamsLair]

One possible solution would be to implement some hacky type-conversion code for the sake of compatibility with TypeInfo, in case anyone (or worse, any .Net classes) attempts to serialize one. It should be done in a small protected static method in the Serializer base class, so its usage can easily be tracked. Maybe name it ConvertToTypeInfo or something.

It would

• Check if the parameter is a Type object.
• Returns (obj as Type).GetTypeInfo() if it is.
• Returns obj as TypeInfo if it isn't.

It would be used for

• Serializer.ReadObject<T>, depending on T.
• Serializer.AssignFieldValue, depending on the fields type.
• XmlSerializer.ReadArray / BinarySerializer.ReadArray for each element, depending on the array type. Do the check outside of the loop though and see if that can be moved to Serializer as well.

A typical usage check would test

• If the object at hand is a Type object.
• If the required object type is not a Type, but deriving from MemberInfo

This should cover all the basic cases.