@pcarrier @benleggiero This is along the lines of what I’m thinking. I’m using Android as an example, where I want to have a custom view, with lazily added subviews. In the onMeasure method I’m looking for some nice way to treat the mutable properties as immutable references for that method, so that I don’t have to do constant null checks. I think this would be useful for any sort of framework with stateful callbacks.