23. Inheritance of mix-ins

#include <string>
class ErrorKeeper : private std::string {
public:
    std::string get_error() const
    { return *this; }

protected:
    ErrorKeeper(){}

    void reset_error()
    { erase(); }

    void set_error( const char* err )
    { std::string::operator=( err ); }

    void set_error( std::string const& err )
    { std::string::operator=( err ); }

};//class ErrorKeeper

class Worker : public ErrorKeeper {
public:
    void run() {
        reset_error();
        // ...
        set_error( "everything ok" );
    }
};//class Worker


#include <cassert>
int main()
{
    Worker main_thread;
    main_thread.run();
    assert(
        main_thread.get_error() == "everything ok"
        );
    return 0;
}