lenv.c

static Table *getcurrenv (lua_State *L) {
  if (L->ci == L->base_ci)  /* no enclosing function? *///如果该函数不是内嵌函数，那么直接返回G表
    return hvalue(gt(L));  /* use global table as environment */
  else {//再则，如果是内嵌函数，就返回其母函数的`env`表
    Closure *func = curr_func(L);
    return func->c.env;
  }
}

LUALIB_API int luaL_ref (lua_State *L, int t) {
  int ref;
  t = abs_index(L, t);
  if (lua_isnil(L, -1)) {
    lua_pop(L, 1);  /* remove from stack */
    return LUA_REFNIL;  /* `nil' has a unique fixed reference */
  }
  lua_rawgeti(L, t, FREELIST_REF);  /* get first free element */
  ref = (int)lua_tointeger(L, -1);  /* ref = t[FREELIST_REF] */
  lua_pop(L, 1);  /* remove it from stack */
  if (ref != 0) {  /* any free element? */
    lua_rawgeti(L, t, ref);  /* remove it from list */
    lua_rawseti(L, t, FREELIST_REF);  /* (t[FREELIST_REF] = t[ref]) */
  }
  else {  /* no free elements */
    ref = (int)lua_objlen(L, t);
    ref++;  /* create new reference */
  }
  lua_rawseti(L, t, ref);
  return ref;
}

LUALIB_API void luaL_unref (lua_State *L, int t, int ref) {
  if (ref >= 0) {
    t = abs_index(L, t);
    lua_rawgeti(L, t, FREELIST_REF);
    lua_rawseti(L, t, ref);  /* t[ref] = t[FREELIST_REF] */
    lua_pushinteger(L, ref);
    lua_rawseti(L, t, FREELIST_REF);  /* t[FREELIST_REF] = ref */
  }
}

static TValue *index2adr (lua_State *L, int idx) {
  if (idx > 0) {
    TValue *o = L->base + (idx - 1);
    api_check(L, idx <= L->ci->top - L->base);
    if (o >= L->top) return cast(TValue *, luaO_nilobject);
    else return o;
  }
  else if (idx > LUA_REGISTRYINDEX) {
    api_check(L, idx != 0 && -idx <= L->top - L->base);
    return L->top + idx;
  }
  else switch (idx) {  /* pseudo-indices */
    case LUA_REGISTRYINDEX: return registry(L);
    case LUA_ENVIRONINDEX: {
      Closure *func = curr_func(L);
      sethvalue(L, &L->env, func->c.env);
      return &L->env;
    }
    case LUA_GLOBALSINDEX: return gt(L);
    default: {
      Closure *func = curr_func(L);
      idx = LUA_GLOBALSINDEX - idx;
      return (idx <= func->c.nupvalues)
                ? &func->c.upvalue[idx-1]
                : cast(TValue *, luaO_nilobject);
    }
  }
}

static const luaL_Reg lualibs[] = {
  {"", luaopen_base},
  {LUA_LOADLIBNAME, luaopen_package},
  {LUA_TABLIBNAME, luaopen_table},
  {LUA_IOLIBNAME, luaopen_io},
  {LUA_OSLIBNAME, luaopen_os},
  {LUA_STRLIBNAME, luaopen_string},
  {LUA_MATHLIBNAME, luaopen_math},
  {LUA_DBLIBNAME, luaopen_debug},
  {NULL, NULL}
};

LUALIB_API void luaL_openlibs (lua_State *L) {
  const luaL_Reg *lib = lualibs;
  for (; lib->func; lib++) {
    lua_pushcfunction(L, lib->func);
    lua_pushstring(L, lib->name);
    lua_call(L, 1, 0);
  }
}

static void base_open (lua_State *L) {
  /* set global _G */
  lua_pushvalue(L, LUA_GLOBALSINDEX);
  lua_setglobal(L, "_G");
  /* open lib into global table */
  luaL_register(L, "_G", base_funcs);
  lua_pushliteral(L, LUA_VERSION);
  lua_setglobal(L, "_VERSION");  /* set global _VERSION */
  /* `ipairs' and `pairs' need auxiliary functions as upvalues */
  auxopen(L, "ipairs", luaB_ipairs, ipairsaux);
  auxopen(L, "pairs", luaB_pairs, luaB_next);
  /* `newproxy' needs a weaktable as upvalue */
  lua_createtable(L, 0, 1);  /* new table `w' */
  lua_pushvalue(L, -1);  /* `w' will be its own metatable */
  lua_setmetatable(L, -2);
  lua_pushliteral(L, "kv");
  lua_setfield(L, -2, "__mode");  /* metatable(w).__mode = "kv" */
  lua_pushcclosure(L, luaB_newproxy, 1);
  lua_setglobal(L, "newproxy");  /* set global `newproxy' */
}

lenv.h

#define lua_ref(L,lock) ((lock) ? luaL_ref(L, LUA_REGISTRYINDEX) : \
      (lua_pushstring(L, "unlocked references are obsolete"), lua_error(L), 0))

#define lua_unref(L,ref)        luaL_unref(L, LUA_REGISTRYINDEX, (ref))

#define lua_getref(L,ref)       lua_rawgeti(L, LUA_REGISTRYINDEX, (ref))

/*
** pseudo-indices
*/
#define LUA_REGISTRYINDEX	(-10000)
#define LUA_ENVIRONINDEX	(-10001)
#define LUA_GLOBALSINDEX	(-10002)
#define lua_upvalueindex(i)	(LUA_GLOBALSINDEX-(i))