[bv-dev] Conflict issue with value extraction and JavaFX collection types

Hi, We are refining the value extraction work and one of the remaining tasks is to throw a proper exception if we have ValueExtractors defined in parallel hierarchies for a given type. This led to discovering the below issue with the JavaFX collection types. Let's take the ListProperty example (we have the same issue with Set and Map): ListProperty inherits from ObservableValue and from List. For now, it uses (by chance) the ObservableValue extractor which unwraps the value by default. So basically: @NotNull private ListProperty<String> listProperty = new ReadOnlyListWrapper<String>( null ); will return a violation. With the new conflict detection, it will throw an exception as it's unable to find ONE most specific ValueExtractor as there are 2 valid candidates: ObservableValueValueExtractor and ListValueExtractor. If we want to solve the conflict, we need to introduce a specific ValueExtractor for ListProperty and decide of its behavior. We have 2 possibilities: 1/ consider ListProperty as an ObservableValue and thus simply unwrap the list and validate the constraint against the list. In the above example, @NotNull would then apply to the inner list. Same behavior as explained above. 2/ consider ListProperty as a List. Thus the value extractor would iterate over the element of the list. In the above case, it won't return a violation. In the below example, the @NotNull would refer to listProperty itself and the constraints on the elements of the list would be validated: @NotNull private ListProperty<@Size(min = 3) String> listProperty = new ReadOnlyListWrapper<String>( null ); Gunnar and I are in favor of 2/ but it changes the current behavior as the @NotNull would refer to the container instead of referring to the wrapped value. We would really like to have some feedback from people using JavaFX. Thanks! -- Guillaume