Component extractors

The individual components of a Duration can be viewed by the `component extractor' operations:

       Duration d = Duration::seconds(-1);
       cout << d.day_part() << "d "
            << d.hour_part() << "h "
            << d.minute_part() << "m "
            << d.second_part() << "s"
            << endl;

which prints

       0d 0h 0m -1s

The fact that Duration arguments are `normalized' means that the values returned by the component extractors satisfy the following invariant:

• hour_part() will always lie in the range [-23,+23]

• minute_part() and second_part() will lie in the range [-59,+59]

• Components will be either (1) all zero, (2) all nonnegative, or (3) all nonpositive.

       Duration d = Duration::hours(1);
   

       cout << seconds(d) << endl;

which prints 3600.

Finally, operator void*() provides a convenient test for zero-length Durations through implicit conversion in contexts like if and loop conditions, which expect integral or pointer values. The following loop depends on implicit conversion for its termination condition:

       for(Duration d = Duration::days(100);
           d;
           d -= Duration::days(1)){
           ...
       }