Accept setting data-provider of subclasses

Not sure if I’m missing some Java generics basics, but why it isn’t possible to set a DataProvider<Bar, ?> to a ComboBox<Foo>, if Bar extends Foo?

In other words, can the signature of HasDataProvider#setDataProvider be changed from:

void setDataProvider(DataProvider<T, ?> dataProvider);

to

void setDataProvider(DataProvider<? extends T, ?> dataProvider);

? It would really simplify the codebase, since now I need a DP for every subtype I have.

[pleku]

@knoobie sure - but this is not a priority in itself and we will not break all data provider components just because of this. In case we need to make breaking things anyway, then we can include this too, but otherwise this is a secondary priority.

For any new added API, we will take this into account and not tie the type parameter like we did earlier.

[pleku]

As now we went with not breaking any existing data providers and partly hiding the data provider as an abstraction level so one does not have use a data provider to set the data to the component (either in-memory or lazy). So while it is still fine to use data providers, it is not mandatory and thus I don’t see this breaking change happening as it would further complicate things.