Implement additional set operators: STLSetUnion, STLSetIntersection and STLIncludes.

base/stl_util.h

Index: base/stl_util.h
diff --git a/base/stl_util.h b/base/stl_util.h
index ccad09d7317b4825045b41a6dbc8c48b14169d67..3602df0377ade5e461c73aad16f672743050b98d 100644
--- a/base/stl_util.h
+++ b/base/stl_util.h
@@ -201,9 +201,11 @@ namespace base {
 // Returns true if the container is sorted.
 template <typename Container>
 bool STLIsSorted(const Container& cont) {
-  return std::adjacent_find(cont.begin(), cont.end(),
-                            std::greater<typename Container::value_type>())
-      == cont.end();
+  // Note: Use reverse iterator on container to ensure we only require
+  // value_type to implement operator<.
+  return std::adjacent_find(cont.rbegin(), cont.rend(),
+                            std::less<typename Container::value_type>())
+      == cont.rend();
 }
 
 // Returns a new ResultType containing the difference of two sorted containers.
@@ -218,6 +220,41 @@ ResultType STLSetDifference(const Arg1& a1, const Arg2& a2) {
   return difference;
 }
 
+// Returns a new ResultType containing the union of two sorted containers.
+template <typename ResultType, typename Arg1, typename Arg2>
+ResultType STLSetUnion(const Arg1& a1, const Arg2& a2) {
+  DCHECK(STLIsSorted(a1));
+  DCHECK(STLIsSorted(a2));
+  ResultType result;
+  std::set_union(a1.begin(), a1.end(),
+                 a2.begin(), a2.end(),
+                 std::inserter(result, result.end()));
+  return result;
+}
+
+// Returns a new ResultType containing the intersection of two sorted
+// containers.
+template <typename ResultType, typename Arg1, typename Arg2>
+ResultType STLSetIntersection(const Arg1& a1, const Arg2& a2) {
+  DCHECK(STLIsSorted(a1));
+  DCHECK(STLIsSorted(a2));
+  ResultType result;
+  std::set_intersection(a1.begin(), a1.end(),
+                        a2.begin(), a2.end(),
+                        std::inserter(result, result.end()));
+  return result;
+}
+
+// Returns true if the sorted container |a1| contains all elements of the sorted
+// container |a2|.
+template <typename Arg1, typename Arg2>
+bool STLIncludes(const Arg1& a1, const Arg2& a2) {
+  DCHECK(STLIsSorted(a1));
+  DCHECK(STLIsSorted(a2));
+  return std::includes(a1.begin(), a1.end(),
+                       a2.begin(), a2.end());
+}
+
 }  // namespace base
 
 #endif  // BASE_STL_UTIL_H_