Re: How do you solve the general missing-value problem?

Sometimes you need to inform that the value is missing. Some use
pointers to objects where NULL represents the missing value. Another
solution is to use boost::optional.

However, sometimes you need to provide more second level information
than just missing value. How do you solve that?

I came up with an idea below. Is that a good solution or are there
better ways to solve it? Does any library have anything similar? What
can be improved? Any feedback is welcome.

enum Signal
{
    NOT_AVAILABLE,
    AVAILABLE,
    WEAK,
    DISTORTED
};

typedef Multivalence<
    double,
    Signal,
    NOT_AVAILABLE,
    AVAILABLE> SignalDouble;

SignalDouble getSample()
{
    //return SignalDouble(); // Missing value.
    return SignalDouble( 8.75 ); // Good value.
    //return SignalDouble( DISTORTED ); // Distorted value.
}

int main( int argc, char* argv[] )
{
    SignalDouble sample = getSample();

    switch( sample )
    {
       case NOT_AVAILABLE:
          std::cout << "No sample available" << std::endl;
          break;

       case AVAILABLE:
          std::cout << "Sample: " << *sample << std::endl;
          break;

       case WEAK:
          std::cout << "Signal too weak" << std::endl;
          break;

       case DISTORTED:
          std::cout << "Signal distorted" << std::endl;
          break;
    }

    return 0;
}