Example for P0083R3 __cpp_lib_node_extract:

void update(std::set<X>& set, const X& elem, int val)
{
  auto pos = set.find(elem);
  if (pos == set.end())
    return;
#if __cpp_lib_node_extract
  auto next = std::next(pos);
  auto x = set.extract(pos);
  x.value().update(val);
  set.insert(next, std::move(x));
#else
  X tmp = *pos;
  pos = set.erase(pos);
  tmp.update(val);
  set.insert(pos, std::move(tmp));
#endif
}

The version using extract() doesn't need to copy or move any X objects
and performs no memory allocation.