Should a base class be marked abstract if there are no abstract members?

Question

Is it okay for a class to be marked as abstract if it has no abstract members? Even if there is no practical reason for to directly instantiate it? (aside from unit tests)

Answer 1

Yes, it is reasonable and beneficial to mark explicitly as abstract a base class that should not be instantiated -- even in the absence of abstract methods.

• It enforces the common guideline to make non-leaf classes abstract.
• It prevents other programmers from creating instances of the class. This may make it easier for you to add abstract methods to it later.

Answer 2

Do you want that class to ever have an actual instance? If yes, then don't mark it abstract. If no, then mark it abstract.