Peter Dimov wrote:
Dave Harris wrote:
But suppose I have pair< pair<int,int>, pair<int,int> > ? Shouldn't that yield the same hash value as int[4] ?
I don't expect a pair< pair<int, int>, pair<int, int> > to be frequently refactored into an int[4]. So no, I don't think that it should necessarily have the same hash value as an int[4]. Similarly, I don't think that vector< vector<int> > should necessarily have the same hash value as its flattened vector<int> counterpart.
They definitely should not for vector< vector<int> >. boost::hash should reflect std::equal_to, and std::equal_to does not flatten sequences. And since we're treating pairs like ranges of two values, nested pairs should mirror nested vectors. Of course, when using a custom equality function object which flattens sequences, a custom hash function with this behaviour is correct.