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author | Marc Mutz <marc.mutz@kdab.com> | 2016-07-11 11:14:34 +0200 |
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committer | Marc Mutz <marc.mutz@kdab.com> | 2016-07-14 06:53:48 +0000 |
commit | c2f4705f23ddccf075010edb0532fd73145b8b15 (patch) | |
tree | e35ca3cde5b3ae81b140dcb3d232067a988ee74e /src/corelib/tools/qhash.cpp | |
parent | 89152c57d864c6767daa5aead2adb3ae6bee482b (diff) |
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>
Diffstat (limited to 'src/corelib/tools/qhash.cpp')
-rw-r--r-- | src/corelib/tools/qhash.cpp | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/src/corelib/tools/qhash.cpp b/src/corelib/tools/qhash.cpp index 593a87e65d..abec9ebb79 100644 --- a/src/corelib/tools/qhash.cpp +++ b/src/corelib/tools/qhash.cpp @@ -2644,4 +2644,24 @@ uint qHash(long double key, uint seed) Q_DECL_NOTHROW \sa QHash::constFind() */ +/*! + \fn uint qHash(const QHash<Key, T> &key, uint seed = 0) + \since 5.8 + \relates QHash + + Returns the hash value for the \a key, using \a seed to seed the calculation. + + Type \c T must be supported by qHash(). +*/ + +/*! + \fn uint qHash(const QMultiHash<Key, T> &key, uint seed = 0) + \since 5.8 + \relates QMultiHash + + Returns the hash value for the \a key, using \a seed to seed the calculation. + + Type \c T must be supported by qHash(). +*/ + QT_END_NAMESPACE |