Slice does not offer a dedicated union construct because it is redundant. By deriving classes from a common base class, you can create the same effect as with a union:
module M
{
class Shape
{
// Definitions for shapes, such as size, center, etc.
}
class Circle extends Shape
{
// Definitions for circles, such as radius...
}
class Rectangle extends Shape
{
// Definitions for rectangles, such as width and length...
}
interface ShapeShifter
{
Shape translate(Shape s, long xDistance, long yDistance);
}
}
The parameter s of the translate operation can be viewed as a union of two members: a Circle and a Rectangle. The receiver of a Shape instance can use the type ID of the instance to decide whether it received a Circle or a Rectangle. Alternatively, if you want something more along the lines of a conventional discriminated union, you can use the following approach:
class UnionDiscriminator
{
int d;
}
class Member1 extends UnionDiscriminator
{
// d == 1
string s;
float f;
}
class Member2 extends UnionDiscriminator
{
// d == 2
byte b;
int i;
}
With this approach, the UnionDiscriminator class provides a discriminator value. The "members" of the union are the classes that are derived from UnionDiscriminator. For each derived class, the discriminator takes on a distinct value. The receiver of such a union uses the discriminator value in a switch statement to select the active union member.