Function lua_copy

xrepo/packages/l/lua/port/lua/src/lapi.c:259–271

LUA_API void lua_copy (lua_State *L, int fromidx, int toidx) {
  TValue *fr, *to;
  lua_lock(L);
  fr = index2value(L, fromidx);
  to = index2value(L, toidx);
  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);
  /* LUA_REGISTRYINDEX does not need gc barrier
     (collector revisits it before finishing collection) */
  lua_unlock(L);
}


LUA_API void lua_pushvalue (lua_State *L, int idx) {