Programming in D – 解答 - 関数のオーバーロードの解答

関数のオーバーロード

次の2つのオーバーロードは、既存のinfo()のオーバーロードを利用している。

void info(Meal meal) {
    info(meal.time);
    write('-');
    info(addDuration(meal.time, TimeOfDay(1, 30)));

    write(" Meal, Address: ", meal.address);
}

void info(DailyPlan plan) {
    info(plan.amMeeting);
    writeln();
    info(plan.lunch);
    writeln();
    info(plan.pmMeeting);
}

これらの型をすべて使用するプログラム全体は、次の通りだ。

import std.stdio;

struct TimeOfDay {
    int hour;
    int minute;
}

void info(TimeOfDay time) {
    writef("%02s:%02s", time.hour, time.minute);
}

TimeOfDay addDuration(TimeOfDay start,
                      TimeOfDay duration) {
    TimeOfDay result;

    result.minute = start.minute + duration.minute;
    result.hour = start.hour + duration.hour;
    result.hour += result.minute / 60;

    result.minute %= 60;
    result.hour %= 24;

    return result;
}

struct Meeting {
    string    topic;
    size_t    attendanceCount;
    TimeOfDay start;
    TimeOfDay end;
}

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

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

struct Meal {
    TimeOfDay time;
    string    address;
}

void info(Meal meal) {
    info(meal.time);
    write('-');
    info(addDuration(meal.time, TimeOfDay(1, 30)));

    write(" Meal, Address: ", meal.address);
}

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

void info(DailyPlan plan) {
    info(plan.amMeeting);
    writeln();
    info(plan.lunch);
    writeln();
    info(plan.pmMeeting);
}

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

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

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

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

    info(todaysPlan);
    writeln();
}

main()関数は、オブジェクトリテラルのみを使用して次のように記述することもできる。

void main() {
    info(DailyPlan(Meeting("Bike Ride", 4,
                           TimeOfDay(10, 30),
                           TimeOfDay(11, 45)),

                   Meal(TimeOfDay(12, 30), "İstanbul"),

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

    writeln();
}