How can I add a type constraint to include anything serializable in a generic method?

Question

My generic method needs to serialize the object passed to it, however just insisting that it implements ISerializable doesn\'t seem to work. For example, I have a struct ret

Answer 1

Instead of

XmlSerializer xmlSerializer = new XmlSerializer(typeof(T));

try

XmlSerializer xmlSerializer = new XmlSerializer(message.GetType());

Answer 2

The only way to know if an object is serializable is to try to serialize it.

In fact, you were asking how to tell if a type "is serializable", but the actual question will be with respect to objects. Some instances of a type may not be serializable even if the type is marked [Serializable]. For instance, what if the instance contains circular references?

Answer 3

You can't do this totally via generic constraints, but you can do a couple things to help:

1) Put the new() constraint on the generic type (to enable the ability to deserialize and to ensure the XmlSerializer doesn't complain about a lack of default ctor):

where T : new()

2) On the first line of your method handling the serialization (or constructor or anywhere else you don't have to repeat it over and over), you can perform this check:

if( !typeof(T).IsSerializable && !(typeof(ISerializable).IsAssignableFrom(typeof(T)) ) )
    throw new InvalidOperationException("A serializable Type is required");

Of course, there's still the possibility of runtime exceptions when trying to serialize a type, but this will cover the most obvious issues.

Answer 4

I wrote a length blog article on this subject that you may find helpful. It mainly goes into binary serialization but the concepts are applicable to most any serialization format.

• http://blogs.msdn.com/jaredpar/archive/2009/03/31/is-it-serializable.aspx

The long and short of it is

• There is no way to add a reliable generic constraint
• The only way to check and see if an object was serializable is to serialize it and see if the operation succeeds