How to generate a compiler warning/error when object sliced

Question

I want to know if it is possible to let compiler issue a warning/error for code as following:

Note:

1. Yea, it is bad programming style and

Answer 1

I would suggest adding a constructor to your base class which takes a const reference to the derived class explicitly (with a forward declaration). In my simple test app, this constructor gets called in the slicing case. You could then at least get a run-time assertion, and you could probably get a compile-time assertion with clever use of templates (eg: instantiate a template in a way which generates a compile-time assertion in that constructor). There may also be compiler-specific ways to get compile time warnings or errors when you call explicit functions; for example, you can use "__declspec(deprecated)" for the "slice constructor" in Visual Studio to get a compile-time warning, at least in the function-call case.

So in your example, the code would look like this (for Visual Studio):

class Base { ...
    __declspec(deprecated) Base( const Derived& oOther )
    {
        // Static assert here if possible...
    }
...

This works in my test (compile-time warning). Note that it doesn't solve the copy case, but a similarly-constructed assignment operator should do the trick there.

Hope this helps. :)