diff --git a/cpp/grains/grains.cpp b/cpp/grains/grains.cpp
deleted file mode 100644
index b7646ff..0000000
--- a/cpp/grains/grains.cpp
+++ /dev/null
@@ -1,56 +0,0 @@
-#include "grains.h"
-
-#include <limits>
-#include <stdexcept>
-
-
-namespace grains {
-
-using namespace std;
-
-
-namespace {
-    
-static const index_t number_of_squares = 64;
-
-template <typename T>
-struct total_as_max
-{
-    static inline T total()
-    {
-        return numeric_limits<T>::max();
-    }
-};
-
-template <typename T>
-struct total_by_shift
-{
-    static inline T total()
-    {
-        return T(1) << number_of_squares - 1;
-    }
-};
-
-static_assert(number_of_squares <= numeric_limits<ulong_t>::digits,
-              "grains::ulong_t is too small for grains::total");
-
-typedef conditional<number_of_squares == numeric_limits<ulong_t>::digits,
-                    total_as_max<ulong_t>,
-                    total_by_shift<ulong_t>>::type total_policy_t;
-}
-
-
-ulong_t square(index_t index)
-{
-    if (index < 1 || index > number_of_squares)
-        throw domain_error("invalid square number");
-
-    return ulong_t(1) << (index - 1);
-}
-
-ulong_t total()
-{
-    return total_policy_t::total();
-}
-
-}
diff --git a/cpp/grains/grains.h b/cpp/grains/grains.h
index 5afadd5..3b9c43b 100644
--- a/cpp/grains/grains.h
+++ b/cpp/grains/grains.h
@@ -3,12 +3,57 @@
 #define EXERCISM_RUN_ALL_TESTS
 
 
-namespace grains {
+#include <limits>
+#include <stdexcept>
 
-typedef unsigned long long ulong_t;
-typedef unsigned int       index_t;
 
-ulong_t square(index_t index);
-ulong_t total();
+template <size_t   number_of_squares = 64,
+          typename ulong_t = unsigned long long>
+class custom_grains
+{
+    typedef typename std::numeric_limits<ulong_t> limits_t;
 
-}
+    static_assert(std::is_unsigned<ulong_t>::value,
+            "ulong_t must be unsigned");
+
+    static_assert(number_of_squares <= limits_t::digits,
+            "ulong_t is too short");
+
+    struct total_as_max
+    {
+        static inline ulong_t total()
+        {
+            return limits_t::max();
+        }
+    };
+
+    struct total_by_shift
+    {
+        static inline ulong_t total()
+        {
+            return ulong_t(1) << number_of_squares - 1;
+        }
+    };
+
+    typedef typename std::conditional<
+        number_of_squares == limits_t::digits,
+        total_as_max,
+        total_by_shift>::type   total_policy_t;
+
+public:
+
+    static ulong_t square(size_t index)
+    {
+        if (index < 1 || index > number_of_squares)
+            throw std::domain_error("invalid square number");
+
+        return ulong_t(1) << (index - 1);
+    }
+
+    static ulong_t total()
+    {
+        return total_policy_t::total();
+    }
+};
+
+typedef custom_grains<> grains;