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Asked: 2026-05-11T08:31:49+00:00

I was reading on the sealed keyword in C#. I cant remember the last

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I was reading on the sealed keyword in C#. I cant remember the last time i inherit from a standard library. In c++ I remember inheriting an std interface that typedef a few types and used some of my parameters. But that is 1) Trivial 2) An interface

From the top of my head, i dont remember any class that i inherited that didnt have a virtual function expecting to be inherited. Can anyone tell me of a situation where you needed to inherit a non trivial class that wasnt an interface?

I might even say its a good rule to thumb not to inherit a class unless it has virtual functions. Is this a good rule of thumb?

NOTE: I use operator SomeClass& SomeClass() { return m_someClass; } in the case i need to pass my object as another class. It works well.

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  1. It is actually used in C++, for all these not-is-a kinds of inheritance (eg. inheriting an implementation, mixins, boost::noncopyable, where you inherit from it and make your class noncopyable, boost::operators where you inherit from some class and it will add some operators to your class). Also, when doing metaprogramming with C++ types, inheriting from another type(s) is one of the simplest methods of composing types.

    Another case where you inherit from a class that doesn’t have virtual functions, but serves as ‘kind of’ an interface, is static polymorphism (techniques like CRTP, where class ConcreteA : BaseA). They don’t need the virtual functions, because everything is resolved at compile-time.

    However, if you want to treat your class runtime-polymorphically, you should really make at least one method virtual, and that would be the destructor. There are exceptions, but rare.

    Even when you have a polymorphic hierarchy, you sometimes derive from concrete classes. One example would be a SingleLineEdit deriving from TextEdit. However, this is a little dangerous, because it breaks encapsulation of the parent class (eg. its methods may expect some implementation details, and you must respect and preserve them in the subclass – which may be tricky, since they are implementation details that may change without notice in the next version etc.)

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