From Lua 5.2: Add luaL_testudata().

Contributed by François Perrad.

src/lauxlib.h

@@ -88,6 +88,7 @@ LUALIB_API void luaL_traceback (lua_State *L, lua_State *L1, const char *msg,
 LUALIB_API void (luaL_setfuncs) (lua_State *L, const luaL_Reg *l, int nup);
 LUALIB_API void (luaL_pushmodule) (lua_State *L, const char *modname,
 				   int sizehint);
+LUALIB_API void *(luaL_testudata) (lua_State *L, int ud, const char *tname);
 
 
 /*

src/lj_api.c

@@ -875,7 +875,7 @@ LUA_API void lua_upvaluejoin(lua_State *L, int idx1, int n1, int idx2, int n2)
   lj_gc_objbarrier(L, fn1, gcref(fn1->l.uvptr[n1]));
 }
 
-LUALIB_API void *luaL_checkudata(lua_State *L, int idx, const char *tname)
+LUALIB_API void *luaL_testudata(lua_State *L, int idx, const char *tname)
 {
   cTValue *o = index2adr(L, idx);
   if (tvisudata(o)) {
@@ -884,8 +884,14 @@ LUALIB_API void *luaL_checkudata(lua_State *L, int idx, const char *tname)
     if (tv && tvistab(tv) && tabV(tv) == tabref(ud->metatable))
       return uddata(ud);
   }
-  lj_err_argtype(L, idx, tname);
-  return NULL;  /* unreachable */
+  return NULL;  /* value is not a userdata with a metatable */
+}
+
+LUALIB_API void *luaL_checkudata(lua_State *L, int idx, const char *tname)
+{
+  void *p = luaL_testudata(L, idx, tname);
+  if (!p) lj_err_argtype(L, idx, tname);
+  return p;
 }
 
 /* -- Object setters ------------------------------------------------------ */