monitor with operator overloading c++

Question

Hi,

I would like to write a wrapper class with all operators overloaded such that I can detect when we write/read or modify its contents. For instance:

probe<int> x;
x = 5;     // write
if(x) {    // read
   x += 7; // modify
}

Anyone already did that? If not which operators must I overload to be sure I dont miss anything?

Answer 1

Use this as a common idea. There are plenty of operators like &= |= [] which maybe are not principal in your case.

template < typename T >
struct monitor
{
    monitor( const T& data ):
        data_( data )
    {
        id_ = get_next_monitor_id(); 
    }

    monitor( const monitor& m )
    {
       id_ = get_next_monitor_id();

       m.notify_read();
       notify_write();

       data_ = m.data_;
    }

    operator T()
    {
        notify_read();
        return data_;    
    }

    monitor& operator = ( const monitor& m )
    {
        m.notify_read();
        notify_write();

        data_ = m.data_;
        return *this;
    }

    monitor& operator += ( const monitor& m )
    {
        m.notify_read();
        notify_write();

        data_ += m.data_;
        return *this;
    }
/*
    operator *=
    operator /=
    operator ++ ();
    operator ++ (int);
    operator -- ();
    operator -- (int);
*/
private:
    int id_;
    T data_;

    void notify_read()
    {
        std::cout << "object " << id_ << " was read" << std::endl;
    }

    void notify_write()
    {
        std::cout << "object " << id_ << " was written" << std::endl;
    }
};

Answer 2

You can't, I think. operator?: isn't overloadable. Also, if T::T(int) is defined, T foo = 4 is legal but T foo = probe<int>(4) isn't. There's at most one user-defined conversion.

Furthermore, because probe is not a POD, the behavior of your program can change.