Smart pointer test in a while loop: use the comma operator?

Question

I recently saw code like this:

// 3rd Party API: (paraphrased)
void APIResetIterator(int ID); // reset iterator for call to next()
Mogrifier* APINext(int ID); // User must delete pointer returned

...

typedef std::unique_ptr<Mogrifier> MogPtr;

...

const it listID = 42;
APIResetIterator(listID);
MogPtr elem;
while (elem.reset(APINext(listID)), elem) {
  // use elem
}

Is this a good idea? Does it work?

---

I'll add the corresponding for loop for easy reference:

for (MogPtr elem(APINext(listID)); elem; elem.reset(APINext(listID));) {
  // use elem
}

... doesn't strike me as really optimal either ...

Answer 1

Maybe we should write it as:

template<class SPT, typename P>
SPT& reset(SPT& smartPtr, P ptr) {
  smartPtr.reset(ptr);
  return smartPtr;
}

for (MogPtr elem; reset(elem, APINext(listID));) {
  // use elem
}