Differential D18758 Diff 58398 kdevplatform/3rdparty/qtpromise/qtpromise-0.5.0/docs/qtpromise/helpers/filter.md

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		1		---
		2		title: filter
		3		---
		4
		5		# QtPromise::filter
		6
		7		Since: 0.4.0
		8
		9		```cpp
		10		QtPromise::filter(Sequence<T> values, Filterer filterer) -> QPromise<Sequence<T>>
		11
		12		// With:
		13		// - Sequence: STL compatible container (e.g. QVector, etc.)
		14		// - Filterer: Function(T value, int index) -> bool
		15		```
		16
		17		Iterates over `values` and [filters the sequence](https://en.wikipedia.org/wiki/Filter_%28higher-order_function%29) to another using the given `filterer` function. If `filterer` returns `true`, a copy of the item is put in the `output` sequence, otherwise, the item will not appear in `output`. If `filterer` throws, `output` is rejected with the new exception.
		18
		19		If `filterer` 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.
		20
		21		```cpp
		22		auto output = QtPromise::filter(QVector{
		23		QUrl("http://a..."),
		24		QUrl("http://b..."),
		25		QUrl("http://c...")
		26		}, [](const QUrl& url, ...) {
		27		return QPromise<bool>([&](auto resolve, auto reject) {
		28		// resolve(true) if 'url' is reachable, else resolve(false)
		29		// {...}
		30		});
		31		});
		32
		33		// 'output' resolves as soon as all promises returned by
		34		// 'filterer' are fulfilled or at least one is rejected.
		35
		36		// 'output' type: QPromise<QVector<QUrl>>
		37		output.then([](const QVector<QUrl>& res) {
		38		// 'res' contains only reachable URLs
		39		});
		40		```
		41
		42		::: tip NOTE
		43		The order of the output sequence values is guarantee to be the same as the original sequence, regardless of completion order of the promises returned by `filterer`.
		44		:::
		45
		46		See also: [`QPromise<T>::filter`](../qpromise/filter.md)