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Advanced Programming Techniques in D

Superclass Members

Explore how to access inherited superclass members in D using the super keyword, disambiguate names in inheritance hierarchies, and properly call superclass constructors from subclasses. Understand the role of super in constructors and how subclass constructors manage superclass initialization for seamless object creation.

We'll cover the following...

Accessing superclass members

The super keyword allows referring to members that are inherited from the superclass.

D
class Clock {
    int hour;
    int minute;
    int second;
    void adjust(int hour, int minute, int second = 0) { 
        this.hour = hour;
        this.minute = minute;
        this.second = second;
    } 
}
class AlarmClock : Clock {
    int alarmHour;
    int alarmMinute;
    
    void adjustAlarm(int hour, int minute) { 
        alarmHour = hour;
        alarmMinute = minute; 
    }
    void foo() {
        super.minute = 10; // The inherited 'minute' member
        minute = 10; // Same thing if there is no ambiguity 
    }
}
void main() {}

The super keyword is not always necessary; minute alone has the same meaning in the code above (line # 23). The super keyword is needed when both the superclass and the subclass have members under the same names.

If multiple classes in an inheritance tree define a symbol with the same name, one can use the specific name of the class in the inheritance tree to disambiguate between the symbols:

D
import std.stdio;



class Device {

    string manufacturer;

}



class Clock : Device {

    string manufacturer;

}



class AlarmClock : Clock { 

    // ...



    void foo() {

        Device.manufacturer = "Sunny Horology, Inc.";

        Clock.manufacturer = "Better Watches, Ltd."; 

    }

}



void main() {

    auto alarmC = new AlarmClock();

    alarmC.foo();

    writeln(alarmC.manufacturer);

}
...