diff options
author | Giuseppe D'Angelo <giuseppe.dangelo@kdab.com> | 2022-03-01 04:24:38 +0100 |
---|---|---|
committer | Giuseppe D'Angelo <giuseppe.dangelo@kdab.com> | 2022-03-04 00:21:44 +0100 |
commit | 0deff80eabd577f3514d255e32f74502c914dfe1 (patch) | |
tree | 353014233bbb87123679ac985de18daee3834341 /src/corelib/tools/qhash.cpp | |
parent | dd5fc20e902187356538d1c993d9ece729f6f505 (diff) |
Associative containers: add a way to obtain a key/value range
Our associative containers' iterator's value_type isn't a destructurable
type (yielding key/value). This means that something like
for (auto [k, v] : map)
doesn't even compile -- one can only "directly" iterate on the
values. For quite some time we've had QKeyValueIterator to allow
key/value iteration, but then one had to resort to a "traditional" for
loop:
for (auto i = map.keyValueBegin(), e = keyValueEnd(); i!=e; ++i)
This can be easily packaged in an adaptor class, which is what this
commmit does, thereby offering a C++17-compatible way to obtain
key/value iteration over associative containers.
Something possibly peculiar is the fact that the range so obtained is
a range of pairs of references -- not a range of references to pairs.
But that's easily explained by the fact that we have no pairs to build
references to; hence,
for (auto &[k, v] : map.asKeyValueRange())
doesn't compile (lvalue reference doesn't bind to prvalue pair).
Instead, both of these compile:
for (auto [k, v] : map.asKeyValueRange())
for (auto &&[k, v] : map.asKeyValueRange())
and in *both* cases one gets references to the keys/values in the map.
If the map is non-const, the reference to the value is mutable.
Last but not least, implement pinning for rvalue containers.
[ChangeLog][QtCore][QMap] Added asKeyValueRange().
[ChangeLog][QtCore][QMultiMap] Added asKeyValueRange().
[ChangeLog][QtCore][QHash] Added asKeyValueRange().
[ChangeLog][QtCore][QMultiHash] Added asKeyValueRange().
Task-number: QTBUG-4615
Change-Id: Ic8506bff38b2f753494b21ab76f52e05c06ffc8b
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Diffstat (limited to 'src/corelib/tools/qhash.cpp')
-rw-r--r-- | src/corelib/tools/qhash.cpp | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/src/corelib/tools/qhash.cpp b/src/corelib/tools/qhash.cpp index e3106745da..b5aaaeee5b 100644 --- a/src/corelib/tools/qhash.cpp +++ b/src/corelib/tools/qhash.cpp @@ -2270,6 +2270,25 @@ size_t qHash(long double key, size_t seed) noexcept \sa constKeyValueBegin() */ +/*! \fn template <class Key, class T> auto QHash<Key, T>::asKeyValueRange() & + \fn template <class Key, class T> auto QHash<Key, T>::asKeyValueRange() const & + \fn template <class Key, class T> auto QHash<Key, T>::asKeyValueRange() && + \fn template <class Key, class T> auto QHash<Key, T>::asKeyValueRange() const && + \since 6.4 + + Returns a range object that allows iteration over this hash as + key/value pairs. For instance, this range object can be used in a + range-based for loop, in combination with a structured binding declaration: + + \snippet code/src_corelib_tools_qhash.cpp 34 + + Note that both the key and the value obtained this way are + references to the ones in the hash. Specifically, mutating the value + will modify the hash itself. + + \sa QKeyValueIterator +*/ + /*! \fn template <class Key, class T> QHash<Key, T>::iterator QHash<Key, T>::erase(const_iterator pos) \since 5.7 @@ -3411,6 +3430,24 @@ size_t qHash(long double key, size_t seed) noexcept \sa constKeyValueBegin() */ +/*! \fn template <class Key, class T> auto QMultiHash<Key, T>::asKeyValueRange() & + \fn template <class Key, class T> auto QMultiHash<Key, T>::asKeyValueRange() const & + \fn template <class Key, class T> auto QMultiHash<Key, T>::asKeyValueRange() && + \fn template <class Key, class T> auto QMultiHash<Key, T>::asKeyValueRange() const && + \since 6.4 + + Returns a range object that allows iteration over this hash as + key/value pairs. For instance, this range object can be used in a + range-based for loop, in combination with a structured binding declaration: + + \snippet code/src_corelib_tools_qhash.cpp 35 + + Note that both the key and the value obtained this way are + references to the ones in the hash. Specifically, mutating the value + will modify the hash itself. + + \sa QKeyValueIterator +*/ /*! \class QMultiHash::iterator \inmodule QtCore |