Utils/Logger: Implement targets

[senf.git] / Utils / mpl.hh

diff --git a/Utils/mpl.hh b/Utils/mpl.hh
index ba60083..761ebf4 100644 (file)
--- a/Utils/mpl.hh
+++ b/Utils/mpl.hh
@@ -39,6 +39,15 @@ namespace mpl {
     /** \defgroup senfmpl Low-level template meta programming helpers
      */
 
+    /** \brief Marker class for empty default values etc.
+
+        This is like Boosts \c boost::mpl::na just an empty class used as template default argument
+        to mark missing arguments 
+        
+        \note Don't use this as an empty base class. We may add some informative members to this.
+     */
+    struct nil {};
+
     /** \brief Return-value type used to implement overload selection
 
         The senf::mpl::rv type is used together with \ref SENF_MPL_RV() to select template
@@ -182,6 +191,17 @@ namespace mpl {
         static senf::mpl::rv<0> _SENF_MPL_SLOT_ ## name (_);                                      \
         SENF_MPL_SLOT_SET(name,value)
 
+    /** \brief Define MPL slot initialized to 0
+
+        This is like \ref SENF_MPL_SLOT_DEF() but initializes the slot to the fixed value 0. The
+        advantage over \ref SENF_MPL_SLOT_DEF() is, that this macro may be called from an include
+        file whereas all the other \\c SENF_MPL_SLOT_ macros must always be called from the relevant
+        file.
+     */
+#   define SENF_MPL_SLOT_DEF_ZERO(name)                                                           \
+        template <class _>                                                                        \
+        static senf::mpl::rv<0> _SENF_MPL_SLOT_ ## name (_);
+
     /** \brief Set MPL slot
         \see \ref SENF_MPL_SLOT_DEF()
         \ingroup senfmpl