Move list with .at into generic in util.h

Instead of repeating making a class that inherits from
std::list, make this gestures::List a single point of
truth for this code.  This is still just a std::list
but adds .at() to this class.

BUG=b:271591258
TEST=USE="coverage" FEATURES="test noclean" emerge-brya chromeos-base/gestures

Change-Id: Id612a6501d5caabea8195b8a14c76c28dcaced5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/gestures/+/4361866
Code-Coverage: Henry Barnor <hbarnor@chromium.org>
Reviewed-by: Harry Cutts <hcutts@chromium.org>
Reviewed-by: Sean O'Brien <seobrien@chromium.org>
Auto-Submit: Denis Brockus <dbrockus@chromium.org>
Tested-by: Denis Brockus <dbrockus@chromium.org>
Commit-Queue: Denis Brockus <dbrockus@chromium.org>

5 files changed, 25 insertions, 49 deletions

diff --git a/include/lookahead_filter_interpreter.h b/include/lookahead_filter_interpreter.h
index c37f170..ba2f92b 100644
--- a/include/lookahead_filter_interpreter.h
+++ b/include/lookahead_filter_interpreter.h
@@ -107,11 +107,7 @@ class LookaheadFilterInterpreter : public FilterInterpreter {
 
   stime_t ExtraVariableDelay() const;
 
-  struct QStateList : public std::list<QState> {
-    QState& at(int offset) {
-      return ListAt<QState>(*this, offset);
-    }
-  } queue_;
+  List<QState> queue_;
 
   // The last id assigned to a contact (part of drumroll suppression)
   short last_id_;
diff --git a/include/metrics_filter_interpreter.h b/include/metrics_filter_interpreter.h
index 9dc1978..816f849 100644
--- a/include/metrics_filter_interpreter.h
+++ b/include/metrics_filter_interpreter.h
@@ -54,12 +54,7 @@ class MetricsFilterInterpreter : public FilterInterpreter {
 
   // struct for one finger's data of one frame.
   typedef State<FingerState, 3> MState;
-
-  struct FingerHistory : public std::list<MState> {
-    MState& at(int offset) {
-      return ListAt<MState>(*this, offset);
-    }
-  };
+  typedef List<MState> FingerHistory;
 
   // Push the new data into the buffer.
   void AddNewStateToBuffer(FingerHistory& history,
diff --git a/include/trend_classifying_filter_interpreter.h b/include/trend_classifying_filter_interpreter.h
index 6c05073..049c5e0 100644
--- a/include/trend_classifying_filter_interpreter.h
+++ b/include/trend_classifying_filter_interpreter.h
@@ -153,11 +153,7 @@ private:
     }
   };
 
-  struct FingerHistory : public std::list<KState> {
-    KState& at(int offset) {
-      return ListAt<KState>(*this, offset);
-    }
-  };
+  typedef List<KState> FingerHistory;
 
   // Trend types for internal use
   enum TrendType {
diff --git a/include/util.h b/include/util.h
index afaf61a..f0c2a39 100644
--- a/include/util.h
+++ b/include/util.h
@@ -95,24 +95,27 @@ inline bool SetContainsValue(const Set& the_set,
 }
 
 template<typename Elem>
-Elem& ListAt(std::list<Elem>& the_list, int offset) {
-  // Traverse to the appropriate offset
-  if (offset < 0) {
-    // negative offset is from end to begin
-    for (auto iter = the_list.rbegin(); iter != the_list.rend(); ++iter) {
-      if (++offset == 0)
-        return *iter;
-    }
-  } else {
-    // positive offset is from begin to end
-    for (auto iter = the_list.begin(); iter != the_list.end(); ++iter) {
-      if (offset-- == 0)
-        return *iter;
+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();
   }
-  // Invalid offset
-  abort();
-}
+};
 
 }  // namespace gestures
 
diff --git a/src/util_unittest.cc b/src/util_unittest.cc
index 9d6bd40..f19fe1f 100644
--- a/src/util_unittest.cc
+++ b/src/util_unittest.cc
@@ -27,11 +27,7 @@ TEST(UtilTest, ListAtTest) {
     int x;
   };
 
-  struct ElemList : public std::list<element> {
-    element& at(int offset) {
-      return ListAt<element>(*this, offset);
-    }
-  } list;
+  List<element> list;
 
   for (auto i = 0; i < kMaxElements; ++i) {
     auto& elem = list.emplace_back();
@@ -53,14 +49,9 @@ TEST(UtilTest, ListAtTest) {
 }
 
 TEST(UtilTest, ListAtDeathForwardTest) {
+  List<int> list;
   const int kMaxElements = 3;
 
-  struct IntList : public std::list<int> {
-    int& at(int offset) {
-      return ListAt<int>(*this, offset);
-    }
-  } list;
-
   for (auto i = 0; i < kMaxElements; ++i) {
     list.emplace_back(i);
   }
@@ -68,14 +59,9 @@ TEST(UtilTest, ListAtDeathForwardTest) {
 }
 
 TEST(UtilTest, ListAtDeathBackwardTest) {
+  List<int> list;
   const int kMaxElements = 3;
 
-  struct IntList : public std::list<int> {
-    int& at(int offset) {
-      return ListAt<int>(*this, offset);
-    }
-  } list;
-
   for (auto i = 0; i < kMaxElements; ++i) {
     list.emplace_back(i);
   }