Question

Timer.h:

template<class T>
class Timer {
    public:
      typedef T Units;

    virtual Units get() = 0;
};

TimerImpl.h:

class TimerImpl: public Timer<long> {
public:

TimerImpl() {
}

~TimerImpl() {

}

long get();

};

FpsMeter.h(version 1):

template <class T> 
class FpsMeter {
    private:
    Timer<T>* timer;

    public:
    FpsMeter (Timer<T>* timer) {
        this->timer = timer;
    }

    ...

};

This example works. But it does not look pretty.

Timer<long>* t = new TimerImpl();
FpsMeter<long>* f1  = new FpsMeter<long> (t);

Here there are a lot of extra template uses. How can I realize this idea of multy-type interface when the type is defined by the implementation and user class has not to define new type, it should use the type of the implementation.

Answer 1

If you don’t mind a helper template function which always creates FpsMeter on the heap you could something like the following

template < class T >
FpsMeter<T> *make_FpsMeter( Timer<T> *timer ) {
  return new FpsMeter<T>( timer );
  }

Then creating a FpsMeter of the appropriate type is like so

FpsMeter<long> *f1 = make_FpsMeter( new TimerImpl() );

Or if you can use C++11 auto you’d get

auto f1 = make_FpsMeter( new TimerImpl() );