message: Some optimizations with reserve()
diff: @@ -31,6 +31,10 @@ V &HeteroVector::get_vec() {
  // don't have it yet, so create functions for copying and destroying
  if (iter == vectors_<T>.end()) {
  + clear_functions_.reserve(4);
  + copy_functions_.reserve(4);
  + move_functions_.reserve(4);
  +
  clear_functions_.emplace_back (
  [](HeteroVector &hv) { vectors_<T>.erase(&hv); });
  