Add qHash(QHash) and qHash(QMultiHash)

The hash function is carefully designed to give the same result
as the straight-forward implementation of qHash(unordered_map),
which we'll probably add at some point, namely: std::accumulate
over a container of std::pair.

This is one reason to use std:: and not QPair in the implemen-
tation of qHash(QHash). The other is that qHash(QPair) uses a
bad hash combiner, which may xor out the 'seed' from the result.

We can't fix that until Qt 6, but the qHash(std::pair) overload
uses the well-known boost::hash_combine algorithm (implemented
in Qt as QtPrivate::QHashCombine), so we can use that.

I also trust std::pair to work without problems with reference
template arguments, while QPair only very recently gained a very
basic auto-test for reference parameters.

[ChangeLog][QtCore] Added qHash() overloads for QHash, QMultiHash.

Change-Id: I90879d8a99cf1aadb6e84ecc0c3704f52f3691da
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

0 files changed, 0 insertions, 0 deletions