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I can reproduce the problem in a simple example that doesn't involve Spring4D (however, I get an "E2010 Incompatible types" error instead of an E2250) : type IShared<T> = reference to function: T; Shared = class class function Make<T: class>(AObj: T): IShared<T>; end; TSharedImpl<T: class> = class(TInterfacedObject, IShared<T>) FObj: T; constructor Create(AObj: T); destructor Destroy; override; function Invoke: T; end; TTest = class end; TTester = class procedure DoTest(AObj: TTest); end; class function Shared.Make<T>(AObj: T): IShared<T>; begin Result := TSharedImpl<T>.Create(AObj) as IShared<T>; end; constructor TSharedImpl<T>.Create(AObj: T); begin inherited Create; FObj := AObj; end; destructor TSharedImpl<T>.Destroy; begin FObj.Free; inherited Destroy; end; function TSharedImpl<T>.Invoke: T; begin Result := FObj; end; procedure TTester.DoTest(AObj: TTest); begin //... end; procedure Foo1; var Tester : IShared<TTester>; TestObj : IShared<TTest>; begin Tester := Shared.Make(TTester.Create); TestObj := Shared.Make(TTest.Create); Tester.DoTest(TestObj); // <-- Compiles OK! end; procedure Foo2; begin var Tester: IShared<TTester>; var TestObj: IShared<TTest>; Tester := Shared.Make(TTester.Create); TestObj := Shared.Make(TTest.Create); Tester.DoTest(TestObj); // <-- E2010 Incompatible types: 'TTest' and 'IShared<TTest>' Tester.DoTest(TestObj()); // <-- Compiles OK! end; I have now reported this issue to Embarcadero: RSS-2613: Anonymous Method is called differently depending on whether it is declared as an Inline Variable or not

Show off 😉 Thanks, I have added it to the bug report.

That is not what I would call a MINIMAL example, but at least it compiles this time. There is still a lot of IRRELEVANT code that has nothing at all to do with demonstrating the issue at hand. But so be it. Your TBaseConnectionParams and TSqliteParams classes are duplicating similar code because THEY ARE RETURNING DIFFERENT THINGS, so how to do you expect one to just inherit the behavior of the other? They can't. If you really want to make use of class inheritance then you need to simplify the design of the common elements so they are coherent and overridable across descendants. You are not even override'ing the base methods, you are reintroduce'ing them. That is not how inheritance works.