mirror of
https://github.com/simonbrunel/qtpromise.git
synced 2025-02-09 08:15:44 +08:00
3c1461b8d0
- Add npm package.json to make easier maintaining dependencies. - Make markdown files consistent using remark. - Wrap markdown lines to 100 characters. - Better README.md layout and visual. - Enable VuePress landing/home page. - Upgrade to latest VuePress version. - Add link to the new Qt Marketplace.
52 lines
1.6 KiB
Markdown
52 lines
1.6 KiB
Markdown
---
|
|
title: map
|
|
---
|
|
|
|
# QtPromise::map
|
|
|
|
*Since: 0.4.0*
|
|
|
|
```cpp
|
|
QtPromise::map(Sequence<T> values, Mapper mapper) -> QPromise<QVector<R>>
|
|
|
|
// With:
|
|
// - Sequence: STL compatible container (e.g. QVector, etc.)
|
|
// - Mapper: Function(T value, int index) -> R | QPromise<R>
|
|
```
|
|
|
|
Iterates over `values` and [maps the sequence](https://en.wikipedia.org/wiki/Map_%28higher-order_function%29)
|
|
to another using the given `mapper` function. The type returned by `mapper` determines the type of
|
|
the `output` promise. If `mapper` throws, `output` is rejected with the new exception.
|
|
|
|
If `mapper` returns a promise (or `QFuture`), the `output` promise is delayed until all the promises
|
|
are resolved. If any of the promises fails, `output` immediately rejects with the error of the
|
|
promise that rejected, whether or not the other promises are resolved.
|
|
|
|
```cpp
|
|
auto output = QtPromise::map(QVector{
|
|
QUrl("http://a..."),
|
|
QUrl("http://b..."),
|
|
QUrl("http://c...")
|
|
}, [](const QUrl& url, ...) {
|
|
return QPromise<QByteArray>([&](auto resolve, auto reject) {
|
|
// download content at url and resolve
|
|
// {...}
|
|
});
|
|
});
|
|
|
|
// 'output' resolves as soon as all promises returned by
|
|
// 'mapper' are fulfilled or at least one is rejected.
|
|
|
|
// 'output' type: QPromise<QVector<QByteArray>>
|
|
output.then([](const QVector<QByteArray>& res) {
|
|
// {...}
|
|
});
|
|
```
|
|
|
|
::: tip NOTE
|
|
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 `mapper`.
|
|
:::
|
|
|
|
See also: [`QPromise<T>::map`](../qpromise/map.md)
|