Hands-On Design Patterns with C++

The Fragile Base Class problem

The Fragile Base Class problem is not limited to the Template Method, but is, to some degree, inherent in all object-oriented languages. The problem arises when changes to the base class break the derived class. To see how this can happen, specifically when using the non-virtual interface, let's go back to the file writer and add the ability to write many strings at once:

class FileWriter {    public:    void Write(const char* data) {        Preamble(data);        ... write data to a file ...        Postscript(data);    }    void Write(std::vector<const char*> huge_data) {        Preamble(huge_data);        for (auto data: huge_data) { ... write data to file ... }        Postscript(huge_data);    }    private: virtual void Preamble(std::vector<const char*> huge_data) ...