qt-everywhere-src-5.15.1/qtbase/src/concurrent/doc/snippets/code/src_concurrent_qtconcurrentfilter.cpp

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//! [0]
bool function(const T &t);
//! [0]


//! [1]
bool allLowerCase(const QString &string)
{
    return string.lowered() == string;
}

QStringList strings = ...;
QFuture<QString> lowerCaseStrings = QtConcurrent::filtered(strings, allLowerCase);
//! [1]


//! [2]
QStringList strings = ...;
QFuture<void> future = QtConcurrent::filter(strings, allLowerCase);
//! [2]


//! [3]
V function(T &result, const U &intermediate)
//! [3]


//! [4]
void addToDictionary(QSet<QString> &dictionary, const QString &string)
{
    dictionary.insert(string);
}

QStringList strings = ...;
QFuture<QSet<QString> > dictionary = QtConcurrent::filteredReduced(strings, allLowerCase, addToDictionary);
//! [4]


//! [5]
QStringList strings = ...;
QFuture<QString> lowerCaseStrings = QtConcurrent::filtered(strings.constBegin(), strings.constEnd(), allLowerCase);

// filter in-place only works on non-const iterators
QFuture<void> future = QtConcurrent::filter(strings.begin(), strings.end(), allLowerCase);

QFuture<QSet<QString> > dictionary = QtConcurrent::filteredReduced(strings.constBegin(), strings.constEnd(), allLowerCase, addToDictionary);
//! [5]


//! [6]
QStringList strings = ...;

// each call blocks until the entire operation is finished
QStringList lowerCaseStrings = QtConcurrent::blockingFiltered(strings, allLowerCase);


QtConcurrent::blockingFilter(strings, allLowerCase);

QSet<QString> dictionary = QtConcurrent::blockingFilteredReduced(strings, allLowerCase, addToDictionary);
//! [6]


//! [7]
// keep only images with an alpha channel
QList<QImage> images = ...;
QFuture<void> alphaImages = QtConcurrent::filter(images, &QImage::hasAlphaChannel);

// retrieve gray scale images
QList<QImage> images = ...;
QFuture<QImage> grayscaleImages = QtConcurrent::filtered(images, &QImage::isGrayscale);

// create a set of all printable characters
QList<QChar> characters = ...;
QFuture<QSet<QChar> > set = QtConcurrent::filteredReduced(characters, &QChar::isPrint, &QSet<QChar>::insert);
//! [7]


//! [8]
// can mix normal functions and member functions with QtConcurrent::filteredReduced()

// create a dictionary of all lower cased strings
extern bool allLowerCase(const QString &string);
QStringList strings = ...;
QFuture<QSet<int> > averageWordLength = QtConcurrent::filteredReduced(strings, allLowerCase, QSet<QString>::insert);

// create a collage of all gray scale images
extern void addToCollage(QImage &collage, const QImage &grayscaleImage);
QList<QImage> images = ...;
QFuture<QImage> collage = QtConcurrent::filteredReduced(images, &QImage::isGrayscale, addToCollage);
//! [8]


//! [9]
bool QString::contains(const QRegularExpression &regexp) const;
//! [9]


//! [12]
QStringList strings = ...;
QFuture<QString> future = QtConcurrent::filtered(list, [](const QString &str) {
    return str.contains(QRegularExpression("^\\S+$")); // matches strings without whitespace
});
//! [12]

//! [13]
struct StartsWith
{
    StartsWith(const QString &string)
    : m_string(string) { }

    typedef bool result_type;

    bool operator()(const QString &testString)
    {
        return testString.startsWith(m_string);
    }

    QString m_string;
};

QList<QString> strings = ...;
QFuture<QString> fooString = QtConcurrent::filtered(strings, StartsWith(QLatin1String("Foo")));
//! [13]

//! [14]
struct StringTransform
{
    void operator()(QString &result, const QString &value);
};

QFuture<QString> fooString =
  QtConcurrent::filteredReduced<QString>(strings,
                                         StartsWith(QLatin1String("Foo")),
                                         StringTransform());
//! [14]