Earlier this month, I wrote about validating temporary models for forms. The validation returned .complete or .incomplete, which doesn’t help much when you want to show what did go wrong. So I came up with a richer validation syntax.
Ian Keen posted an article about type-safe temporary models. You would use them like scratch pad contexts in Core Data: in forms, you collect information into these temporary models and then generate your real objects from them.
One thing that repeatedly messes up the conceptual purity of a view model is figuring out which entity should be mutated upon user interaction. Part of this purity stems from the fact that a view model is best served as view data to stress that it doesn’t contain much (business) logic. Making the data mutable introduces a lot of problems figuring out what that view model really is.