Reduce template arguments.

src/book/bbo_listener.h

@@ -7,12 +7,13 @@
 namespace liquibook { namespace book {
 
 /// @brief generic listener of top-of-book events
-template <class OrderBook, class DepthTracker >
+template <class OrderBook>
 class BboListener {
 public:
   /// @brief callback for top of book change
-  virtual void on_bbo_change(const OrderBook* book, 
-                             const DepthTracker* depth) = 0;
+  virtual void on_bbo_change(
+      const OrderBook* book, 
+      const typename OrderBook::DepthTracker* depth) = 0;
 };
 
 } }

src/book/depth_listener.h

@@ -9,12 +9,13 @@
 namespace liquibook { namespace book {
 
 /// @brief listener of depth events
-template <class OrderBook, class DepthTracker >
+template <class OrderBook>
 class DepthListener {
 public:
   /// @brief callback for change in tracked aggregated depth
-  virtual void on_depth_change(const OrderBook* book, 
-                               const DepthTracker* depth) = 0;
+  virtual void on_depth_change(
+      const OrderBook* book, 
+      const typename OrderBook::DepthTracker* depth) = 0;
 };
 
 } }

src/book/depth_order_book.h

@@ -21,8 +21,8 @@ class DepthOrderBook : public OrderBook<OrderPtr> {
 public:
   typedef Depth<SIZE> DepthTracker;
   typedef DepthOrderBook<OrderPtr, SIZE> MyClass;
-  typedef BboListener<MyClass, DepthTracker > TypedBboListener;
-  typedef DepthListener<MyClass, DepthTracker > TypedDepthListener;
+  typedef BboListener<MyClass > TypedBboListener;
+  typedef DepthListener<MyClass > TypedDepthListener;
   typedef Callback<OrderPtr> DobCallback;
 
   /// @brief construct