Member Functions - D Programming Language
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# Member Functions

#### Member Functions Dersi Problem Çözümleri

1. Potentially negative intermediate values make `decrement()` slightly more complicated than `increment()`:

       struct TimeOfDay {
           // ...

           void decrement(Duration duration) {
               auto minutesToSubtract = duration.minute % 60;
               auto hoursToSubtract = duration.minute / 60;

               minute -= minutesToSubtract;

               if (minute < 0) {
                   minute += 60;
                   ++hoursToSubtract;
               }

               hour -= hoursToSubtract;

               if (hour < 0) {
                   hour = 24 - (-hour % 24);
               }
           }

           // ...
       }

2. To see how much easier it gets with `toString()` member functions, let's look at the `Meeting` overload of `info()` one more time:

       void info(Meeting meeting) {
           info(meeting.start);
           write('-');
           info(meeting.end);

           writef(" \"%s\" meeting with %s attendees",
                  meeting.topic,
                  meeting.attendanceCount);
       }

   Taking advantage of the already-defined `TimeOfDay.toString`, the implementation of `Meeting.toString` becomes trivial:

           string toString() {
               return format("%s-%s \"%s\" meeting with %s attendees",
                             start, end, topic, attendanceCount);
           }

   Here is the entire program:

       import std.stdio;
       import std.string;

       struct Duration {
           int minute;
       }

       struct TimeOfDay {
           int hour;
           int minute;

           string toString() {
               return format("%02s:%02s", hour, minute);
           }

           void increment(Duration duration) {
               minute += duration.minute;

               hour += minute / 60;
               minute %= 60;
               hour %= 24;
           }
       }

       struct Meeting {
           string    topic;
           int       attendanceCount;
           TimeOfDay start;
           TimeOfDay end;

           string toString() {
               return format("%s-%s \"%s\" meeting with %s attendees",
                             start, end, topic, attendanceCount);
           }
       }

       struct Meal {
           TimeOfDay time;
           string    address;

           string toString() {
               TimeOfDay end = time;
               end.increment(Duration(90));

               return format("%s-%s Meal, Address: %s",
                             time, end, address);
           }
       }

       struct DailyPlan {
           Meeting amMeeting;
           Meal    lunch;
           Meeting pmMeeting;

           string toString() {
               return format("%s\n%s\n%s",
                             amMeeting,
                             lunch,
                             pmMeeting);
           }
       }

       void main() {
           auto bikeRideMeeting = Meeting("Bike Ride", 4,
                                          TimeOfDay(10, 30),
                                          TimeOfDay(11, 45));

           auto lunch = Meal(TimeOfDay(12, 30), "İstanbul");

           auto budgetMeeting = Meeting("Budget", 8,
                                        TimeOfDay(15, 30),
                                        TimeOfDay(17, 30));

           auto todaysPlan = DailyPlan(bikeRideMeeting,
                                       lunch,
                                       budgetMeeting);

           writeln(todaysPlan);
           writeln();
       }

   The output of the program is the same as the earlier one that has been using `info()` function overloads:

       10:30-11:45 "Bike Ride" meeting with 4 attendees
       12:30-14:00 Meal, Address: İstanbul
       15:30-17:30 "Budget" meeting with 8 attendees

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