D LanguageClasses

Syntax

  • class Foo { } // inherits from Object
  • class Bar: Foo { } // Bar is a Foo too
  • Foo f = new Foo(); // instantiate new objects on the heap

Remarks

See the specification, browse a book chapter on classes, inheritance and play interactively.

Inheritance

class Animal
{
    abstract int maxSize(); // must be implemented by sub-class
    final float maxSizeInMeters() // can't be overridden by base class
    {
        return maxSize() / 100.0;
    }
}

class Lion: Animal
{
    override int maxSize() { return 350; }
}

void main()
{
    import std.stdio : writeln;
    auto l = new Lion();
    assert(l.maxSizeInMeters() == 3.5);

    writeln(l.maxSizeInMeters()); // 3.5
}

Instantiation

class Lion
{
    private double weight; // only accessible with-in class

    this(double weight)
    {
        this.weight = weight;
    }

    double weightInPounds() const @property // const guarantees no modifications
    // @property functions are treated as fields
    {
        return weight * 2.204;
    }
}

void main()
{
    import std.stdio : writeln;
    auto l = new Lion(100);
    assert(l.weightInPounds == 220.4);

    writeln(l.weightInPounds); // 220.4
}