diff --git a/luprex/cpp/core/luastack.hpp b/luprex/cpp/core/luastack.hpp
index 255cf21f..6edbc988 100644
--- a/luprex/cpp/core/luastack.hpp
+++ b/luprex/cpp/core/luastack.hpp
@@ -146,6 +146,7 @@
 #include "wrap-string.hpp"
 #include "wrap-set.hpp"
 #include <cstring>
+#include <type_traits>
 
 #include "lua.h"
 #include "lauxlib.h"
@@ -277,6 +278,34 @@ class LuaCoreStack : public eng::nevernew {
 protected:
     lua_State *L_;
 
+protected:
+    struct Counts {
+        int nret;
+        int narg;
+        int nvar;
+        constexpr Counts(int r, int a, int v) : nret(r), narg(a), nvar(v) {}
+    };
+
+    template<int NRET, int NARG, int NVAR, class... SS>
+    constexpr static Counts count_slots(LuaRet &v, SS & ... stackslots)
+    {
+        return count_slots<NRET+1, NARG, NVAR>(stackslots...);
+    }
+    template<int NRET, int NARG, int NVAR, class... SS>
+    constexpr static Counts count_slots(LuaArg &v, SS & ... stackslots)
+    {
+        return count_slots<NRET, NARG+1, NVAR>(stackslots...);
+    }
+    template<int NRET, int NARG, int NVAR, class... SS>
+    constexpr static Counts count_slots(LuaVar &v, SS & ... stackslots)
+    {
+        return count_slots<NRET, NARG, NVAR+1>(stackslots...);
+    }
+    template<int NRET, int NARG, int NVAR>
+    constexpr static Counts count_slots() {
+        return Counts(NRET, NARG, NVAR);
+    }
+
 private:
     // Push any value on the stack, by type.
     void push_any_value(LuaNewTableMarker s) const { lua_newtable(L_); }
@@ -529,23 +558,23 @@ private:
     void assign_slots(int argp, int varp, int retp) {}
 
     template<int NARG, int NVAR, int NRET, class... SS>
-    void count_slots(LuaArg &v, SS & ... stackslots)
+    void count_slotsx(LuaArg &v, SS & ... stackslots)
     {
-        count_slots<NARG+1, NVAR, NRET>(stackslots...);
+        count_slotsx<NARG+1, NVAR, NRET>(stackslots...);
     }
     template<int NARG, int NVAR, int NRET, class... SS>
-    void count_slots(LuaVar &v, SS & ... stackslots)
+    void count_slotsx(LuaVar &v, SS & ... stackslots)
     {
-        count_slots<NARG, NVAR+1, NRET>(stackslots...);
+        count_slotsx<NARG, NVAR+1, NRET>(stackslots...);
     }
     template<int NARG, int NVAR, int NRET, class... SS>
-    void count_slots(LuaRet &v, SS & ... stackslots)
+    void count_slotsx(LuaRet &v, SS & ... stackslots)
     {
-        count_slots<NARG, NVAR, NRET+1>(stackslots...);
+        count_slotsx<NARG, NVAR, NRET+1>(stackslots...);
     }
 
     template<int NARG, int NVAR, int NRET>
-    void count_slots() {
+    void count_slotsx() {
         narg_ = NARG;
         nret_ = NRET;
         nvar_ = NVAR;
@@ -565,7 +594,7 @@ private:
 public:
     template<class... SS>
     LuaOldStack(lua_State *L, SS & ... stackslots) : LuaCoreStack(L) {
-        count_slots<0, 0, 0>(stackslots...);
+        count_slotsx<0, 0, 0>(stackslots...);
         if (lua_gettop(L) < narg_) {
             luaL_error(L, "not enough arguments to function");
         }
@@ -621,65 +650,42 @@ public:
 class LuaDefStack : public LuaCoreStack {
 private:
     int nret_;
-    int narg_;
-    int nvar_;
 
-    template<class... SS>
-    void assign_slots(int retp, int argp, int varp, LuaRet &v, SS & ... stackslots) {
-        v.index_ = retp;
-        assign_slots(retp+1, argp, varp, stackslots...);
+    template<int RETP, int ARGP, int VARP, class... SS>
+    void assign_slots(LuaRet &v, SS & ... stackslots) {
+        v.index_ = RETP;
+        assign_slots<RETP+1, ARGP, VARP>(stackslots...);
     }
-    template<class... SS>
-    void assign_slots(int retp, int argp, int varp, LuaArg &v, SS & ... stackslots) {
-        v.index_ = argp;
-        assign_slots(retp, argp + 1, varp, stackslots...);
+    template<int RETP, int ARGP, int VARP, class... SS>
+    void assign_slots(LuaArg &v, SS & ... stackslots) {
+        v.index_ = ARGP;
+        assign_slots<RETP, ARGP+1, VARP>(stackslots...);
     }
-    template<class... SS>
-    void assign_slots(int retp, int argp, int varp, LuaVar &v, SS & ... stackslots) {
-        v.index_ = varp;
-        assign_slots(retp, argp, varp+1, stackslots...);
-    }
-    void assign_slots(int retp, int argp, int varp) {}
-
-    template<int NRET, int NARG, int NVAR, class... SS>
-    void count_slots(LuaRet &v, SS & ... stackslots)
-    {
-        count_slots<NRET+1, NARG, NVAR>(stackslots...);
-    }
-    template<int NRET, int NARG, int NVAR, class... SS>
-    void count_slots(LuaArg &v, SS & ... stackslots)
-    {
-        count_slots<NRET, NARG+1, NVAR>(stackslots...);
-    }
-    template<int NRET, int NARG, int NVAR, class... SS>
-    void count_slots(LuaVar &v, SS & ... stackslots)
-    {
-        count_slots<NRET, NARG, NVAR+1>(stackslots...);
+    template<int RETP, int ARGP, int VARP, class... SS>
+    void assign_slots(LuaVar &v, SS & ... stackslots) {
+        v.index_ = VARP;
+        assign_slots<RETP, ARGP, VARP+1>(stackslots...);
     }
     template<int NRET, int NARG, int NVAR>
-    void count_slots() {
-        nret_ = NRET;
-        narg_ = NARG;
-        nvar_ = NVAR;
-    }
+    void assign_slots() {}
 
 public:
     template<class... SS>
-    LuaDefStack(lua_State *L, SS & ... stackslots) : LuaCoreStack(L) {
-        count_slots<0, 0, 0>(stackslots...);
-        if (lua_gettop(L_) != narg_) {
-            luaL_error(L_, "function expects exactly %d arguments", narg_);
+    inline LuaDefStack(lua_State *L, SS & ... stackslots) : LuaCoreStack(L) {
+        constexpr Counts counts = count_slots<0, 0, 0>(stackslots...);
+        if (lua_gettop(L_) != counts.narg) {
+            luaL_error(L_, "function expects exactly %d arguments", counts.narg);
         }
-        int tot = narg_ + nvar_ + nret_;
-        lua_checkstack(L, tot + 20);
-        for (int i = 0; i < nret_; i ++) {
+        lua_checkstack(L, counts.narg + counts.nvar + counts.nret + 20);
+        for (int i = 0; i < counts.nret; i ++) {
             lua_pushnil(L_);
             lua_insert(L_, i + 1);
         }
-        for (int i = 0; i < nvar_; i++) {
+        for (int i = 0; i < counts.nvar; i++) {
             lua_pushnil(L_);
         }
-        assign_slots(1, 1 + nret_, 1 + nret_ + narg_, stackslots...);
+        assign_slots<1, 1 + counts.nret, 1 + counts.nret + counts.narg>(stackslots...);
+        nret_ = counts.nret;
     }
 
     int result() {
@@ -713,7 +719,6 @@ public:
 class LuaExtStack : public LuaCoreStack {
 private:
     int oldtop_;
-    int nvar_;
 
     template<class... SS>
     void assign_slots(int varp, LuaVar &v, SS & ... stackslots) {
@@ -722,38 +727,22 @@ private:
     }
     void assign_slots(int varp) {}
 
-    template<int NVAR, class... SS>
-    void count_slots(LuaVar &v, SS & ... stackslots)
-    {
-        count_slots<NVAR+1>(stackslots...);
-    }
-    template<int NVAR>
-    void count_slots() {
-        nvar_ = NVAR;
-    }
-
 public:
     template<class... SS>
     LuaExtStack(lua_State *L, SS & ... stackslots) : LuaCoreStack(L) {
-        count_slots<0>(stackslots...);
-        lua_checkstack(L_, nvar_ + 20);
+        constexpr Counts counts = count_slots<0, 0, 0>(stackslots...);
+        static_assert(counts.narg == 0, "LuaExtStack doesn't allow LuaArg parameters");
+        static_assert(counts.nret == 0, "LuaExtStack doesn't allow LuaRet parameters");
+        lua_checkstack(L_, counts.nvar + 20);
         oldtop_ = lua_gettop(L_);
-        for (int i = 0; i < nvar_; i++) {
+        for (int i = 0; i < counts.nvar; i++) {
             lua_pushnil(L_);
         }
         assign_slots(oldtop_ + 1, stackslots...);
     }
 
     template<class... SS>
-    LuaExtStack(const LuaCoreStack &LS0, SS & ... stackslots) : LuaCoreStack(LS0.state()) {
-        count_slots<0>(stackslots...);
-        lua_checkstack(L_, nvar_ + 20);
-        oldtop_ = lua_gettop(L_);
-        for (int i = 0; i < nvar_; i++) {
-            lua_pushnil(L_);
-        }
-        assign_slots(oldtop_ + 1, stackslots...);
-    }
+    LuaExtStack(const LuaCoreStack &LS0, SS & ... stackslots) : LuaCoreStack(LS0.state(), stackslots...) {}
 
     ~LuaExtStack() {
         if (!lua_isthrowing(L_)) {