Hide the inherited members like spin() from cell and heptagon.

We don't want `c1->spin(d)` to compile, but we do want `c1->c().spin(d)`
to compile. Make the CRTP inheritance private and make `->c()` the
magic incantation to poke through that privateness.

Author: Quuxplusone

locations.cpp

@@ -127,9 +127,11 @@ template<class T> struct walker;
 int gmod(int i, int j);
 
 template<class CRTP, class T>
-class trailing_connection_table {
-
-  CRTP *crtp() { return static_cast<CRTP*>(this); }
+class connection_table_details {
+  CRTP *crtp() {
+    static_assert(std::is_base_of<connection_table_details, CRTP>::value, "");
+    return static_cast<CRTP*>(this);
+    }
   T **move_table() {
     static_assert(alignof(CRTP) >= alignof(T*), "");
     return (T **)(crtp() + 1);
@@ -139,13 +141,6 @@ class trailing_connection_table {
     }
 
 public:
-  static size_t tailored_alloc_size(int degree) {
-    return sizeof(CRTP) + (degree * sizeof(T*)) + degree;
-    }
-
-  trailing_connection_table& c() { return *this; }
-  const trailing_connection_table& c() const { return *this; }
-
   /** \brief for the edge d, set the `spin` and `mirror` attributes */
   void setspin(int d, int spin, bool mirror) { 
     unsigned char& c = spin_table()[d];
@@ -183,6 +178,18 @@ class trailing_connection_table {
     }
   };
 
+template<class CRTP, class T>
+class trailing_connection_table : private connection_table_details<CRTP, T> {
+public:
+  friend class connection_table_details<CRTP, T>;
+
+  connection_table_details<CRTP, T>& c() { return *this; }
+
+  static size_t tailored_alloc_size(int degree) {
+    return sizeof(CRTP) + (degree * sizeof(T*)) + degree;
+    }
+  };
+
 /** \brief Allocate a class T with a connection_table, but with only `degree` connections. 
  *
  *  Also set yet unknown connections to NULL.