How to write qHash for a QSet container?

Question

I need to implement a set of sets in my application. Using QSet with a custom class requires providing a qHash() function and an operator==.

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Answer 1

A common way to hash containers is to combine the hashes of all elements. Boost provides hash_combine and hash_range for this purpose. This should give you an idea how to implement this for the results of your qHash.

So, given your qHash for Custom:

uint qHash(const QSet& c) {
  uint seed = 0;

  for(auto x : c) {
    seed ^= qHash(x) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
  }

  return seed;
}