Custom types for dumps()

[mdbenito]

As far as I can tell, currently the only branch in udump() that allows serialization of custom types goes through TaggedElement. One must subclass this and implement __str__(). IMO this is problematic for two reasons:

1. One may not control the class definition at all so that subclassing is not an option.
2. Using __str__ for EDN serialization might be undesirable. Very often one wants simpler representations for debugging from this method.
3. It is not always the case that a custom type must be tagged. One can of course just not return any, but that makes the semantics of TaggedElement confusing.

I think all of these can be overcome by allowing registering custom handlers for arbitrary types, exactly in the same manner that @tag does. These would be based on type instead of string. One could add some syntactic sugar with a decorator as well.

Or is there some other way I missed?

[bfontaine]

The simplest implementation would probably be an optional default parameter like json.dump that would be called on objects unsupported by the serializer.