1 files changed, 30 insertions, 18 deletions

diff --git a/include/util.h b/include/util.h
index 2e87a7b..f0c2a39 100644
--- a/include/util.h
+++ b/include/util.h
@@ -5,6 +5,7 @@
 #ifndef GESTURES_UTIL_H_
 #define GESTURES_UTIL_H_
 
+#include <list>
 #include <map>
 #include <set>
 
@@ -61,28 +62,16 @@ bool MapContainsKey(const Map& the_map, const Key& the_key) {
 }
 
 // Removes any ids from the map that are not finger ids in hs.
-// This implementation supports returning removed elements for
-// further processing.
-template<typename Data>
-void RemoveMissingIdsFromMap(std::map<short, Data>* the_map,
-                             const HardwareState& hs,
-                             std::map<short, Data>* removed) {
-  removed->clear();
-  for (typename std::map<short, Data>::const_iterator it =
-      the_map->begin(); it != the_map->end(); ++it)
-    if (!hs.GetFingerState((*it).first))
-      (*removed)[it->first] = it->second;
-  for (typename std::map<short, Data>::const_iterator it =
-      removed->begin(); it != removed->end(); ++it)
-    the_map->erase(it->first);
-}
-
-// Removes any ids from the map that are not finger ids in hs.
 template<typename Data>
 void RemoveMissingIdsFromMap(std::map<short, Data>* the_map,
                              const HardwareState& hs) {
   std::map<short, Data> removed;
-  RemoveMissingIdsFromMap(the_map, hs, &removed);
+  for (const auto& [key, value] : *the_map) {
+    if (!hs.GetFingerState(key))
+      removed[key] = value;
+  }
+  for (const auto& [key, value] : removed)
+    the_map->erase(key);
 }
 
 // Removes any ids from the set that are not finger ids in hs.
@@ -105,6 +94,29 @@ inline bool SetContainsValue(const Set& the_set,
   return the_set.find(elt) != the_set.end();
 }
 
+template<typename Elem>
+class List : public std::list<Elem> {
+public:
+  Elem& at(int offset) {
+    // Traverse to the appropriate offset
+    if (offset < 0) {
+      // negative offset is from end to begin
+      for (auto iter = this->rbegin(); iter != this->rend(); ++iter) {
+        if (++offset == 0)
+          return *iter;
+      }
+    } else {
+      // positive offset is from begin to end
+      for (auto iter = this->begin(); iter != this->end(); ++iter) {
+        if (offset-- == 0)
+          return *iter;
+      }
+    }
+    // Invalid offset
+    abort();
+  }
+};
+
 }  // namespace gestures
 
 #endif  // GESTURES_UTIL_H_