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  1. Qt
  2. QTBUG-88450

QtConcurrent filter/map does not work with move-only output sequences

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    • Icon: Bug Bug
    • Resolution: Unresolved
    • Icon: P3: Somewhat important P3: Somewhat important
    • None
    • 6.0
    • Core: QtConcurrent
    • None

      While QtConcurrent map/filter functions can work with move-only input sequences, they cannot work with move-only output sequences. This implies that copyable output sequences are copied, even though there is no fundamental reason to do so.

      Note that this Jira-Item is about copyable items in move-only containers. It is not about move-only items.

      Reproducer:

      void tst_QtConcurrentFilterMapGenerated::test1()
{
    /* test for
    template<typename OutputSequence, typename InputSequence, typename MapFunctor>
    OutputSequence blockingMapped(QThreadPool* pool, InputSequence && sequence, MapFunctor
    function);

    with
      inputsequence=moveonly
      inputsequencepassing=rvalue
      inputitemtype=standard
      outputsequence=moveonly
      maptype=same
      mappeditemtype=standard
      mapfunction=functor
      mapfunctionpassing=lvalue
    */

    QThreadPool pool;
    pool.setMaxThreadCount(1);

    auto map = MyMap<SequenceItem<tag_input>, SequenceItem<tag_input>> {};

    auto result = QtConcurrent::blockingMapped(
            &pool,
            []() {
                MoveOnlyVector<SequenceItem<tag_input>> result;
                result.push_back(SequenceItem<tag_input>(1, true));
                result.push_back(SequenceItem<tag_input>(2, true));
                result.push_back(SequenceItem<tag_input>(3, true));
                result.push_back(SequenceItem<tag_input>(4, true));
                result.push_back(SequenceItem<tag_input>(5, true));
                result.push_back(SequenceItem<tag_input>(6, true));
                return result;
            }(),
            map);

    auto expected_result = []() {
        MoveOnlyVector<SequenceItem<tag_input>> result;
        result.push_back(SequenceItem<tag_input>(2, true));
        result.push_back(SequenceItem<tag_input>(4, true));
        result.push_back(SequenceItem<tag_input>(6, true));
        result.push_back(SequenceItem<tag_input>(8, true));
        result.push_back(SequenceItem<tag_input>(10, true));
        result.push_back(SequenceItem<tag_input>(12, true));
        return result;
    }();

    QCOMPARE(result, expected_result);
}

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            cnn Qt Core & Network
            andreasbuhr Andreas Buhr
            Vladimir Minenko Vladimir Minenko
            Alex Blasche Alex Blasche
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              Created:
              Updated:

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