[hibernate-dev] Evolvement of SPIs

Hi, related to my earlier mail on deprecations there's another thought I'd like to discuss. When evolving an SPI (typically *implemented* by clients), other restrictions apply than when evolving an API (typically *used* by clients). More specifically, it's no problem to add new methods to an API interface (existing clients continue to function without changes), while that's not true for SPI interfaces (existing implementations break). AFAIK there are basically two approaches for handling the evolvement of SPIs. One is to use use abstract classes instead of interfaces for SPI types. This allows to add new methods in future versions as long as a sensible default implementation in the abstract class can be provided. Implementation classes can override that default implementation if they want to. The other approach is to create a new interface extending the existing one in order to add new methods: public interface Foo { void bar(); } public interface Foo2 extends Foo { void baz(); } Clients implement the latest version they are aware of and want to support. For our own code this means that we have to perform some instanceof calls to determine the version of the passed SPI types. My question now is, whether you got any recommendations for this. Do you have any experience with either approach in other Hibernate projects? Thanks, --Gunnar