/// <summary>
/// Computes an upper bound in the type hierarchy for the set of argument types.
/// This upper bound is a type that all types in the list are assignable to.
/// If the types are all classes, then *the* least-upper-bound in the class
/// hierarchy is returned.
/// If the types contain at least one interface, then *a* deepest upper-bound
/// is found from the intersection of the upward closure of each type.
/// Note that if one of the types is System.Object, then that is immediately
/// returned as the unified type without further examination of the list.
/// </summary>
/// <param name="ts">A list containing the set of types from which to compute the unified type.</param>
/// <returns>The type corresponding to the least-upper-bound.</returns>
public virtual TypeNode UnifiedType(TypeNodeList ts, TypeViewer typeViewer){
if (ts == null || ts.Count == 0) return null;
TypeNode unifiedType = SystemTypes.Object; // default unified type
bool atLeastOneInterface = false;
#region If at least one of the types is System.Object, then that is the unified type
for (int i = 0, n = ts.Count; i < n; i++){
TypeNode t = this.Unwrap(ts[i]);
if (t == SystemTypes.Object){
return SystemTypes.Object;
}
}
#endregion If at least one of the types is System.Object, then that is the unified type
// assert forall{TypeNode t in ts; t != SystemTypes.Object};
#region See if any of the types are interfaces
for (int i = 0, n = ts.Count; i < n; i++){
TypeNode t = this.Unwrap(ts[i]);
if (t.NodeType == NodeType.Interface){
atLeastOneInterface = true;
break;
}
}
#endregion See if any of the types are interfaces
#region Find the LUB in the class hierarchy (if there are no interfaces)
if (!atLeastOneInterface){
TrivialHashtable h = new TrivialHashtable(ts.Count);
// Create the list [s, .., t] for each element t of ts where for each item
// in the list, t_i, t_i = t_{i+1}.BaseType. (s.BaseType == SystemTypes.Object)
// Store the list in a hashtable keyed by t.
// Do this only for classes. Handle interfaces in a different way because of
// multiple inheritance.
for (int i = 0, n = ts.Count; i < n; i++){
TypeNodeList tl = new TypeNodeList();
TypeNode t = this.Unwrap(ts[i]);
tl.Add(t);
TypeNode t2 = t.BaseType;
while (t2 != null && t2 != SystemTypes.Object){ // avoid including System.Object in the list for classes
tl.Insert(t2,0);
t2 = this.Unwrap(t2.BaseType);
}
h[ts[i].UniqueKey] = tl;
}
bool stop = false;
int depth = 0;
while (!stop){
TypeNode putativeUnifiedType = null;
int i = 0;
int n = ts.Count;
putativeUnifiedType = ((TypeNodeList) h[ts[0].UniqueKey])[depth];
while (i < n){
TypeNode t = ts[i];
TypeNodeList subTypes = (TypeNodeList) h[t.UniqueKey];
if (subTypes.Count <= depth || subTypes[depth] != putativeUnifiedType){
// either reached the top of the hierarchy for t_i or it is on a different branch
// than the current one.
stop = true;
break;
}
i++;
}
if (i == n){ // made it all the way through: all types are subtypes of the current one
unifiedType = putativeUnifiedType;
}
depth++;
}
}
#endregion Find the LUB in the class hierarchy (if there are no interfaces)
#region Find *a* LUB in the interface hierarchy (if there is at least one interface or current LUB is object)
if (unifiedType == SystemTypes.Object || atLeastOneInterface){
TrivialHashtable interfaces = new TrivialHashtable();
for (int i = 0, n = ts.Count; i < n; i++){
InterfaceList il = new InterfaceList();
interfaces[ts[i].UniqueKey] = il;
this.SupportedInterfaces(ts[i],il,typeViewer); // side-effect: il gets added to
}
// interfaces[ts[i]] is the upward closure of all of the interfaces supported by ts[i]
// compute the intersection of all of the upward closures
// might as well start with the first type in the list ts
InterfaceList intersection = new InterfaceList();
InterfaceList firstIfaceList = (InterfaceList)interfaces[ts[0].UniqueKey];
for (int i = 0, n = firstIfaceList.Count; i < n; i++){
Interface iface = firstIfaceList[i];
bool found = false;
int j = 1; // start at second type in the list ts
while (j < ts.Count){
InterfaceList cur = (InterfaceList)interfaces[ts[j].UniqueKey];
found = false;
for (int k = 0, p = cur.Count; k < p; k++){
if (cur[k] == iface){
found = true;
break;
}
}
if (!found){
// then the j-th type doesn't support iface, don't bother looking in the rest
break;
}
j++;
}
if (found){
intersection.Add(iface);
}
}
// TODO: take the "deepest" interface in the intersection.
// "deepest" means that if any other type in the intersection is a subtype
// of it, then *don't* consider it.
if (intersection.Count > 0){
InterfaceList finalIntersection = new InterfaceList(intersection.Count);
Interface iface = intersection[0];
for (int i = 0, n = intersection.Count; i < n; i++){
Interface curFace = intersection [i];
int j = 0;
int m = intersection.Count;
while (j < m){
if (j != i){
Interface jFace = intersection[j];
if (TypeViewer.GetTypeView(typeViewer, jFace).IsAssignableTo(curFace))
break;
}
j++;
}
if (j == m){ // made it all the way through, no other iface is a subtype of curFace
finalIntersection.Add(curFace);
}
}
if (finalIntersection.Count > 0){
unifiedType = finalIntersection[0]; // heuristic: just take the first one
}
}
}
#endregion Find *a* LUB in the interface hierarchy (if there is at least one interface or current LUB is object)
return unifiedType;
}
