Hi LA
I guess why many C programming teams avoid virtual keyword is because this innocent-looking keyword can cause complexity explosion when mixed with other elements --
- dynamic cast for pointer or reference variables
- pure virtual functions
- slicing -- without virtual, slicing is more consistent and easier to debug
- passing a RTTI object by reference -- note an object is an RTTI object IFF it has a virtual pointer.
- throwing an RTTI exception object by reference, by pointer or by value -- again, things are simpler without virtual
- member function hiding (by accident) -- without virtual, the hiding rule is simpler
- non-trivial destructors
- pointer delete -- for example, deleting a derived object via a base pointer is undefined behavior if the destructor is non-virtual. If you avoid virtual completely, we would less likely write this kind of buggy code.
- double pointers -- pointer to pointer to an RTTI object
- double dispatch -- usually involves virtual functions. Double-dispatch may not be very meaningful to non-RTTI objects.
- container of RTTI objects, such as vector of pointer-to-base, where each pointee can be a Derived1 object or Derived2 object... -- again, non-RTTI cases are simpler
- templates -- remember STL internally uses no virtual function, and perhaps very little inheritance
- smart pointers holding RTTI objects
- private inheritance
- multiple and virtual inheritance
Some experts advocate all base classes should have virtual destructor. In that case, avoiding virtual means avoiding inheritance. That would definitely reduce complexity.
Tuesday, March 6, 2012
virtual function adding complexity (letter to friend
Labels: original_content, polymorphic/vptr
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