[xsd-users] xsd bypasses customized types

[Ray Lischner]

We are only now starting the transition to xsd 3.2 (just in time for 3.3!), and we are running into a small problem.

We customized a number of types. For example, we have a type CUnsignedInt, which is a restriction of an XML string. The customized type parses the string as a C-style integer and can treat the resulting object as an integer. When serialized to CDR, the customized type stores a binary integer instead of a string.

This worked fine in xsd 2.3, but causes problems in xsd 3.2.

Among the new features is that any string-based type gets some new constructors, including a default constructor. If a schema derives a type from a string-based type, the derived type get those same constructors.

Thus, if a schema derives a type from our CUnsignedInt type, that derived type gets a default constructor that invokes its base class's default constructor. We never defined a default constructor for CUnsignedInt, but we can add one to initialize the numeric value to zero.

More serious is that the code generation does not generate a from-base constructor, that is, one cannot construct an instance of the derived type from an instance of CUnsignedInt. This makes it considerably harder to construct an instance of the derived type from an integer. The developer would have to convert the integer to a string, and use the string as the argument to the constructor.

This violates the principles of the CUnsignedInt type, which looks and acts as an integer (from the developer's point of view). Only when serializing and parsing XML does CUnsignedInt reveal its string nature.

I don't mind it when new features change the way I need to write my customized types. I understand that I must accommodate my customizations. But this change breaks all the code that uses my customization. I cannot shield users from the change by modifying my customization.

So what can we do? At this time, we are considering modifying the xsd compiler to add a switch that would disable the new code that inhibits the from-base constructors and inserts the new string-based constructors. But is that the best solution? Thanks for the help.

Ray Lischner,
Senior Member of Technical Staff
133 National Business Pkwy, Ste 150     t. 443.539.3448
Annapolis Junction, MD 20701                c. 410.854.5170
rlischner at proteuseng.com                     f. 443.539.3370

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