Abstract base type for IMaterializationInterceptor, possibly other interceptor interfaces

[kjkrum]

The docs for interceptor interfaces suggest extending their abstract base types instead of directly implementing the interface. IMaterializationInterceptor is missing a corresponding abstract base type. Some interfaces, like ISingletonInterceptor, have no abstract base type because they have no methods. Others, like IIdentityResolutionInterceptor, have multiple abstract base types. I think MaterializationInterceptor is the only one missing, but please check that.

Why this matters

#27625 added default method implementations for all interceptor interface methods. Interfaces with default method implementations do not play nicely with Visual Studio. There is no suggestion to implement the interface because you don't have to. There is no "generate override" refactoring because your implementation is not an override. You have to manually write the correct method signatures or copy-paste them from the docs or decompiled definition. When extending an abstract base class, you can use the "generate override" refactoring.

[roji]

Interfaces with default method implementations do not play nicely with Visual Studio.

Yes, when EF was starting out, default method implementations (DIM) didn't exist yet, so we had abstract types; when DIM was introduced, we switched to it for simplification.

I don't think we'd add an abstract base class just because Visual Studio supports DIM a bit less nicely; DIM are a fully supported C# language feature, and the degree of support of an IDE isn't cause to not use it. If you think VS's support is lacking, I'd suggest opening a ticket with VS themselves, describing the problems you see.

[kjkrum]

@roji The purpose of DIM is to allow adding methods to published interfaces. It should only be used for that purpose. VS aside, DIM still behaves differently than normal interface implementations in that it requires calling the default methods via the interface rather than the class type. IMO, #27625 was a mistake that could and should be corrected in a future major version.

[roji]

The purpose of DIM is to allow adding methods to published interfaces. It should only be used for that purpose.

Where does this rule come from? What's the advantage of adding an abstract base class in addition to an interface, if the same can be done without doing that?

DIM still behaves differently than normal interface implementations in that it requires calling the default methods via the interface rather than the class type.

Yep, but does that matter in this case?