Serialization requirements

If you want to serialize/deserialize objects to/from MessagePack stream, there are some requirements for the target type.

Requirements

As a rule of thumb, how to determine whether the type is supported is simple: when the type can be serealized with DataContractSerializer, it should be sereialized by the MessagePack serealizer.

More strictly speaking, there are following requirements for target type.

• A type has default public constructor, it has the constructor which take one Int32 parameter only if the type implements IList, it is array, or it is CLI primitive value type.
• A type is concrete type and is not delegate type, that is, type is value type, non-abstract class, enum type. Abstract classes and interfaces cannot be serialized.
• All members (fields and/or properties) are public and are not read only. Note that there are exceptions for collection type member. See following section.
• All fields in the type follows above 2 rules.

Note that you can serialize/deserialize any types even if they are not met to above requirements with your own custom serializer.

Serialization Rule Details

Selecting Properties or Fields

1. All public instance properties and fields are selected as candidates.
2. If there are members which are marked with MessagePackMemberAttribute in candidates, then these members are selected. Otherwise, go next.
3. If the type is marked with DataContractAttribute and there are members which are marked with DataMemberAttribute in candidates, then these members are selected. Otherwise, go next.
4. Members which are NOT marked with NonSerializedAttribute are selected.

Handling Collection

MessagePack for CLI treats collection type members in special manner. If the member type which implements IEnumerable<T> and it has the member which its signature is TReturn Add(T) or void Add(T). It is considered as collection type. If the member is collection type, the member has not to be writeable. Even if the member is initonly or does not have a setter, the serializer can deserialize collection items as long as following conition is true:

• The collection type is not fixed, typically is not an array.
• The collection instance is not read only. Namely, ICollection.IsReadOnly or ICollection<T>.IsReadOnly returns false.

Handling Enums

Enums are serialized as string based on the name of the value. It is most interoperable.

Handling MessagePackObject

It will be packed as is.

Handling System.Object

It will be treated as boxed MessagePackObject. If it is not, the exception will be thrown.