@@ -1,5 +1,5 @@
 /*
-** $Id: lapi.c,v 2.292 2018/06/01 17:40:38 roberto Exp roberto $
+** $Id: lapi.c,v 2.293 2018/06/15 17:30:52 roberto Exp roberto $
 ** Lua API
 ** See Copyright Notice in lua.h
 */
@@ -37,13 +37,10 @@ const char lua_ident[] =
   "$LuaAuthors: " LUA_AUTHORS " $";
 
 
-/* value at a non-valid index */
 
-static const TValue nonvalidvaluep = {NILCONSTANT};
-#define NONVALIDVALUE		cast(TValue *, &nonvalidvaluep)
+/* test for a valid index */
+#define isvalid(L, o)	(!ttisnil(o) || o != &G(L)->nilvalue)
 
-/* corresponding test */
-#define isvalid(o)	((o) != &nonvalidvaluep)
 
 /* test for pseudo index */
 #define ispseudo(i)		((i) <= LUA_REGISTRYINDEX)
@@ -57,7 +54,7 @@ static TValue *index2value (lua_State *L, int idx) {
   if (idx > 0) {
     StkId o = ci->func + idx;
     api_check(L, idx <= L->ci->top - (ci->func + 1), "unacceptable index");
-    if (o >= L->top) return NONVALIDVALUE;
+    if (o >= L->top) return &G(L)->nilvalue;
     else return s2v(o);
   }
   else if (!ispseudo(idx)) {  /* negative index */
@@ -70,10 +67,10 @@ static TValue *index2value (lua_State *L, int idx) {
     idx = LUA_REGISTRYINDEX - idx;
     api_check(L, idx <= MAXUPVAL + 1, "upvalue index too large");
     if (ttislcf(s2v(ci->func)))  /* light C function? */
-      return NONVALIDVALUE;  /* it has no upvalues */
+      return &G(L)->nilvalue;  /* it has no upvalues */
     else {
       CClosure *func = clCvalue(s2v(ci->func));
-      return (idx <= func->nupvalues) ? &func->upvalue[idx-1] : NONVALIDVALUE;
+      return (idx <= func->nupvalues) ? &func->upvalue[idx-1] : &G(L)->nilvalue;
     }
   }
 }
@@ -225,7 +222,7 @@ LUA_API void lua_copy (lua_State *L, int fromidx, int toidx) {
   lua_lock(L);
   fr = index2value(L, fromidx);
   to = index2value(L, toidx);
-  api_check(l, isvalid(to), "invalid index");
+  api_check(l, isvalid(L, to), "invalid index");
   setobj(L, to, fr);
   if (isupvalue(toidx))  /* function upvalue? */
     luaC_barrier(L, clCvalue(s2v(L->ci->func)), fr);
@@ -251,7 +248,7 @@ LUA_API void lua_pushvalue (lua_State *L, int idx) {
 
 LUA_API int lua_type (lua_State *L, int idx) {
   const TValue *o = index2value(L, idx);
-  return (isvalid(o) ? ttype(o) : LUA_TNONE);
+  return (isvalid(L, o) ? ttype(o) : LUA_TNONE);
 }
 
 
@@ -296,7 +293,7 @@ LUA_API int lua_isuserdata (lua_State *L, int idx) {
 LUA_API int lua_rawequal (lua_State *L, int index1, int index2) {
   const TValue *o1 = index2value(L, index1);
   const TValue *o2 = index2value(L, index2);
-  return (isvalid(o1) && isvalid(o2)) ? luaV_rawequalobj(o1, o2) : 0;
+  return (isvalid(L, o1) && isvalid(L, o2)) ? luaV_rawequalobj(o1, o2) : 0;
 }
 
 
@@ -323,7 +320,7 @@ LUA_API int lua_compare (lua_State *L, int index1, int index2, int op) {
   lua_lock(L);  /* may call tag method */
   o1 = index2value(L, index1);
   o2 = index2value(L, index2);
-  if (isvalid(o1) && isvalid(o2)) {
+  if (isvalid(L, o1) && isvalid(L, o2)) {
     switch (op) {
       case LUA_OPEQ: i = luaV_equalobj(L, o1, o2); break;
       case LUA_OPLT: i = luaV_lessthan(L, o1, o2); break;
 
@@ -1,5 +1,5 @@
 /*
-** $Id: lobject.h,v 2.144 2018/06/01 17:40:38 roberto Exp roberto $
+** $Id: lobject.h,v 2.145 2018/06/15 14:14:20 roberto Exp roberto $
 ** Type definitions for Lua objects
 ** See Copyright Notice in lua.h
 */
@@ -144,9 +144,6 @@ typedef StackValue *StkId;  /* index to stack elements */
 #define ttisstrictnil(o)	checktag((o), LUA_TNIL)
 
 
-/* macro defining a nil value */
-#define NILCONSTANT	{NULL}, LUA_TNIL
-
 #define setnilvalue(obj) settt_(obj, LUA_TNIL)
 
 
 
@@ -1,5 +1,5 @@
 /*
-** $Id: lstate.c,v 2.152 2018/05/29 18:02:51 roberto Exp roberto $
+** $Id: lstate.c,v 2.153 2018/06/01 17:40:38 roberto Exp roberto $
 ** Global State
 ** See Copyright Notice in lua.h
 */
@@ -345,6 +345,7 @@ LUA_API lua_State *lua_newstate (lua_Alloc f, void *ud) {
   g->twups = NULL;
   g->totalbytes = sizeof(LG);
   g->GCdebt = 0;
+  setnilvalue(&g->nilvalue);
   setgcparam(g->gcpause, LUAI_GCPAUSE);
   setgcparam(g->gcstepmul, LUAI_GCMUL);
   g->gcstepsize = LUAI_GCSTEPSIZE;
 
@@ -1,5 +1,5 @@
 /*
-** $Id: lstate.h,v 2.157 2018/02/25 12:43:52 roberto Exp roberto $
+** $Id: lstate.h,v 2.158 2018/03/16 15:33:34 roberto Exp roberto $
 ** Global State
 ** See Copyright Notice in lua.h
 */
@@ -148,6 +148,7 @@ typedef struct global_State {
   lu_mem GCestimate;  /* an estimate of the non-garbage memory in use */
   stringtable strt;  /* hash table for strings */
   TValue l_registry;
+  TValue nilvalue;  /* a nil value */
   unsigned int seed;  /* randomized seed for hashes */
   lu_byte currentwhite;
   lu_byte gcstate;  /* state of garbage collector */
 
@@ -1,5 +1,5 @@
 /*
-** $Id: ltm.c,v 2.68 2018/06/01 17:40:38 roberto Exp roberto $
+** $Id: ltm.c,v 2.69 2018/06/08 19:06:59 roberto Exp roberto $
 ** Tag methods
 ** See Copyright Notice in lua.h
 */
@@ -69,7 +69,6 @@ const TValue *luaT_gettm (Table *events, TMS event, TString *ename) {
 
 
 const TValue *luaT_gettmbyobj (lua_State *L, const TValue *o, TMS event) {
-  static const TValue nilobject = {NILCONSTANT};
   Table *mt;
   switch (ttype(o)) {
     case LUA_TTABLE:
@@ -81,7 +80,7 @@ const TValue *luaT_gettmbyobj (lua_State *L, const TValue *o, TMS event) {
     default:
       mt = G(L)->mt[ttype(o)];
   }
-  return (mt ? luaH_getshortstr(mt, G(L)->tmname[event]) : &nilobject);
+  return (mt ? luaH_getshortstr(mt, G(L)->tmname[event]) : &G(L)->nilvalue);
 }