# QtPromise::each

Since: 0.4.0

QtPromise::each(Sequence<T> values, Functor functor) -> QPromise<Sequence<T>>

// With:
// - Sequence: STL compatible container (e.g. QVector, etc.)
// - Functor: Function(T value, int index) -> void | QPromise<void>

Calls the given functor on each element in values then resolves to the original sequence unmodified. If functor throws, output is rejected with the new exception.

If functor returns a promise (or QFuture), the output promise is delayed until all the promises are resolved. If any of the promises fail, output immediately rejects with the error of the promise that rejected, whether or not the other promises are resolved.

auto output = QtPromise::each(QVector<QUrl>{
    QUrl("http://a..."),
    QUrl("http://b..."),
    QUrl("http://c...")
}, [](const QUrl& url, ...) {
    return QPromise<void>{[&](auto resolve, auto reject) {
        // process url asynchronously ...
    }};
});

// `output` resolves as soon as all promises returned by
// `functor` are fulfilled or at least one is rejected.

// output type: QPromise<QVector<QUrl>>
output.then([](const QVector<QUrl>& res) {
    // 'res' contains the original values
});