Interpreting version parameters

[ansharlubis]

1. Associate version on a package basis

2. Define requirements for version variables

public requirement Invertible {
  for class Point { Point inverse(); }
}

public class Line ver 1 «V,W requires Invertible» {
  public Point#V# p1;
  public Point#W# p2;
  public Line(Point#V# p1, Point#W# p2) {
    this.p1 = p1; this.p2 = p2;
  }
  public «Y» Line«V,Y» rotate() {
    return new Line«V,Y»(p1, p2.«Y»inverse());
  }
}

With requirements, checking can be done easily without having to infer constraints. Also, it can make it easier to understand.