Using inheritance to add functionality

Question

I'm using an abstract base class to add logging functionality to all of my classes. It looks like this:

class AbstractLog
{
public:
    virtual ~AbstractLog() = 0;

protected:
    void LogException(const std::string &);

private:
    SingletonLog *m_log;    // defined elsewhere - is a singleton object
};

The LogException() method writes the text to the log file defined in the SingletonLog object, and then throws an exception.

I then use this as my base class for all subsequent classes (there can be hundreds/thousands of these over hundreds of libraries/DLLs).

This allows me to call LogException() wherever I would normally throw an exception.

My question is whether or not this is good design/practice.

P.S.: I'm using inheritance simply to add functionality to all of my classes, not to implement any sort of polymorphism. On top of this, the concept of all of my classes having an is-a relationship with the AbstractLog class is arguable (each class is-a loggable object? Well, yes I suppose they are, but only because I've made them so).

Answer 1

What you suggesting will work, I think better is to create log class ( inheriting from this interface ) and use it as in a way composition ( using interface ) than inheritance - composition is weaker connection between your logic class and log class. The best practice is the less class does the better. Additional benefit is that you will be able to extend log functionality any time you want without modification of business logic.

About this singleton, maybe proxy pattern is better ?

Hope, I helped :)