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QItemSelection: fix a quadratic loop

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QList::erase(it) is a linear operation. Calling it in a loop
constitutes quadratic behavior.

Fix by using the erase-remove idiom.

Write a generic function object QtFunctionObjects::IsNotValid, instead
of a lambda, because I am building up a collection of such function
objects in my tree, to be submitted any time now™, so this will reduce
the churn once that gets merged. Wrap it in the unnamed namespace to
avoid ODR violations in case this pattern repeats.

Replace an existing erase-remove idiom's isNotValid lambda function
with the new function object.

Change-Id: I4f0af04e7b201eb168e79beeda332eee3c6f33c3
Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
This commit is contained in:
Marc Mutz 2017-05-17 14:40:05 +02:00
parent 33c59be551
commit 6d44fa53e1
1 changed files with 20 additions and 12 deletions
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32
src/corelib/itemmodels/qitemselectionmodel.cpp
View File

@ -1267,6 +1267,21 @@ void QItemSelectionModel::select(const QModelIndex &index, QItemSelectionModel::
convenience.
*/
namespace {
namespace QtFunctionObjects {
struct IsNotValid {
typedef bool result_type;
struct is_transparent : std::true_type {};
template <typename T>
Q_DECL_CONSTEXPR bool operator()(T &t) const Q_DECL_NOEXCEPT_EXPR(noexcept(t.isValid()))
{ return !t.isValid(); }
template <typename T>
Q_DECL_CONSTEXPR bool operator()(T *t) const Q_DECL_NOEXCEPT_EXPR(noexcept(t->isValid()))
{ return !t->isValid(); }
};
}
} // unnamed namespace
/*!
Selects the item \a selection using the specified \a command, and emits
selectionChanged().
@ -1290,13 +1305,9 @@ void QItemSelectionModel::select(const QItemSelection &selection, QItemSelection
// be too late if another model observer is connected to the same modelReset slot and is invoked first
// it might call select() on this selection model before any such QItemSelectionModelPrivate::_q_modelReset() slot
// is invoked, so it would not be cleared yet. We clear it invalid ranges in it here.
QItemSelection::iterator it = d->ranges.begin();
while (it != d->ranges.end()) {
if (!it->isValid())
it = d->ranges.erase(it);
else
++it;
}
using namespace QtFunctionObjects;
d->ranges.erase(std::remove_if(d->ranges.begin(), d->ranges.end(), IsNotValid()),
d->ranges.end());
QItemSelection old = d->ranges;
old.merge(d->currentSelection, d->currentCommand);
@ -1748,12 +1759,9 @@ const QItemSelection QItemSelectionModel::selection() const
selected.merge(d->currentSelection, d->currentCommand);
// make sure we have no invalid ranges
// ### should probably be handled more generic somewhere else
auto isNotValid = [](const QItemSelectionRange& range) {
return !range.isValid();
};
using namespace QtFunctionObjects;
selected.erase(std::remove_if(selected.begin(), selected.end(),
isNotValid),
IsNotValid()),
selected.end());
return selected;
}