Chris Jefferson wrote:
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.
Just to comment on this specifically, you really, really should have a vector<vector<int> > hash to the same value as it's flatterned conterpart.
Just to clarify, did you mean "should not have" here? Because...
I have previously written a program where i had a set of vector<vector<int> >s, where when flatterned they were all the same, and I don't think it's that uncommon..
... this part seems to imply that these vectors should not have the same hash value, or the unordered_set will degrade into a linked list.