aspect SubclassCrossRefs {
    // Fill in cross-references for
	// - superclass -> subclasses
	// - TODO: handle implements relation
	// - TODO: handle sub/super-interfaces

	// *** API ***
	
	// A ClassDecl has a *subclasses()* attribute, containing references to the declarations of its subclasses.
	// Currently emulated by a method.
	// syn Collection ClassDecl.subclasses();
	

	// *** Implementation ***
	
	// In future versions of JastAdd the *subclasses* attribute might be implemented
	// using an explicit construct for jointly evaluated collection attributes.
	
	// Emulated implementation of jointly evaluated collection attribute
	public Collection ClassDecl.subclasses() {
		Program root = getProgram();
		if (!root.subclassCrossRefsFilledIn) {
		   root.fillInSubclassCrossRefs();
		   root.subclassCrossRefsFilledIn = true;
		}
		return privateSubclasses;
	}
	
	private LinkedList ClassDecl.privateSubclasses = new LinkedList();
	
	boolean Program.subclassCrossRefsFilledIn = false;
	
	void ASTNode.fillInSubclassCrossRefs() {
		for(int i=0; i<getNumChild(); i++) {
			getChild(i).fillInSubclassCrossRefs();
		}
	}
	
	void ClassDecl.fillInSubclassCrossRefs() {
		if (hasSuperClassAccess()) {
			TypeDecl superClass = getSuperClassAccess().type();
			if (superClass instanceof ClassDecl) {
				((ClassDecl) superClass).privateSubclasses.add(this);
			}
		}
		super.fillInSubclassCrossRefs();
	}
	
}