You are right, but I think it might be solved. In a response to Corion, I wrote:

Perhaps the contructor could be modified. The current hashref would fall under a key named "params" and a different key named "groups" would list group validations. Then, as soon as an accessor is called, the "group" validations would be checked. This would eliminate the order dependence. Workable?

When an accessor is called, the parameters are validated. If a value is never set, we can still validate it when the accessor is called. This is still not foolproof, but I think it's a reasonable scheme. Let me know if you think there are problems with this.

Cheers,
Ovid

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