Comment 5 for bug 532488

After discussion on the mailing list and in the context of another bug, Dale King pointed out that the source of the problem is that a constraint expression is resolved by Assert.That on it's first use and a pointer to the resolved constraint is what is actually used. What we should do for a reusable constraint is to pre-resolve it and then save that pointer.

Note that the problem does not arise with simple constraints like Is.Null. It's only when the constraint has pending operators to be resolved - like Is.Not.Null - that we see the issue.

Requiring the user to resolve the constraint first seems like too much. The Resolve() method is an explicit interface implementation and so requires a cast for it even to be called. I'll experiment with a wrapper class that allows reuse and add some info about reuse to the docs.