1 files changed, 43 insertions, 0 deletions
diff --git a/src/tools/xcode-common/java/com/google/devtools/build/xcode/util/Difference.java b/src/tools/xcode-common/java/com/google/devtools/build/xcode/util/Difference.java
new file mode 100644
index 0000000000..54bd567f28
--- /dev/null
+++ b/src/tools/xcode-common/java/com/google/devtools/build/xcode/util/Difference.java
@@ -0,0 +1,43 @@
+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.xcode.util;
+
+import com.google.common.collect.Sets;
+
+import java.util.Set;
+
+/**
+ * Provides utility methods that make difference operations type safe.
+ *
+ * {@link Sets#difference(Set, Set)} requires no type bound on the second set, which has led to
+ * calls which can never subtract any elements because the set being subtracted cannot contain any
+ * elements which may exist in the first set.
+ */
+public class Difference {
+  private Difference() {
+    throw new UnsupportedOperationException("static-only");
+  }
+
+  /**
+   * Returns the elements in set1 which are not in set2. set2 may contain extra elements which will
+   * be ignored.
+   *
+   * @param set1 Set whose elements to return
+   * @param set2 Set whose elements are to be subtracted
+   */
+  public static <T> Set<T> of(Set<T> set1, Set<T> set2) {
+    return Sets.difference(set1, set2);
+  }
+}