Played with macros for a more convenient header registration system

src/http_headers.cc

@@ -20,6 +20,13 @@ namespace {
     std::unordered_map<std::string, Registry::RegistryFunc> registry;
 }
 
+RegisterHeader(Accept);
+RegisterHeader(ContentLength);
+RegisterHeader(ContentType);
+RegisterHeader(Host);
+RegisterHeader(ContentEncoding);
+RegisterHeader(UserAgent);
+
 void
 Registry::registerHeader(std::string name, Registry::RegistryFunc func)
 {
@@ -133,19 +140,6 @@ Collection::getImpl(const std::string& name) const {
     return std::make_pair(true, it->second);
 }
 
-namespace {
-    struct AtInit {
-        AtInit() {
-            Registry::registerHeader<ContentLength>();
-            Registry::registerHeader<ContentType>();
-            Registry::registerHeader<Host>();
-            Registry::registerHeader<Accept>();
-            Registry::registerHeader<UserAgent>();
-            Registry::registerHeader<ContentEncoding>();
-        }
-    } atInit;
-}
-
 } // namespace Header
 
 } // namespace Http

src/http_headers.h

@@ -101,6 +101,27 @@ struct Registry {
     static bool isRegistered(const std::string& name);
 };
 
+template<typename H>
+struct Registrar {
+    static_assert(IsHeader<H>::value, "Registrar only works with header types");
+
+    Registrar() {
+        Registry::registerHeader<H>();
+    }
+};
+
+/* Crazy macro machinery to generate a unique variable name
+ * Don't touch it !
+ */
+#define CAT(a, b) CAT_I(a, b)
+#define CAT_I(a, b) a ## b
+
+#define UNIQUE_NAME(base) CAT(base, __LINE__)
+
+#define RegisterHeader(Header) \
+    Registrar<Header> UNIQUE_NAME(CAT(CAT_I(__, Header), __))
+
+
 } // namespace Header
 
 } // namespace Http