Re: "Uh, what do I need this for" (was RE: XML.COM: How I LearnedtoLove daBomb)

[John Cowan <jcowan@reutershealth.com>]

Leigh Dodds wrote:

> One side effect of immutable Value objects I noted recently when
> adding a SOAP interface to one of our components, was that I couldn't
> take advantage of the Apache SOAP support for automated (de-)serialisation
> of JavaBeans. Value objects aren't JavaBeans because everything is
> done in the constructor, and there are no set methods.

The cure for that is to add a volatile boolean xxxIsSet field
for every regular field.  The normal constructor sets all these to
true, whereas the Bean (parameterless) constructor sets them all to
false.

Each setXxx method throws an Error if xxxIsSet is true; otherwise
it sets the regular field to the given value and xxxIsSet to true.
This gives immutable semantics while being bean-serialization
compatible, since the deserializer calls each set method exactly once.

It would be useful to write a preprocessor to insert the xxxIsSet
fields and the setXxx methods.

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