在期货中使用flatmap的例子

Question

我无法理解如何在Future中使用flatMap。 '为'看起来很好。

object ConcurrencyExample extends App {
val gpf= Future {gpf operations}
val ccf = Future{ccf operations}

//how can I convert this for to flatMap?
val atbf = for {g <- gpf
c <- ccf }  yield {atbf operations}

Await.result(atbf,1000 millis )
 }

Answer 1

理解的

可以去除flatMap，filter和for { foo <- FooF bar <- BarF(foo) baz <- BazF if bar > 0 bow <- BowF(baz) } yield (baz + 1) 。

这是你如何做到的。

FooF.flatMap { foo => //inner bindings become flatMap
  BarF(foo).flatMap { bar =>
    BazF.filter { baz => baz > 0 } //guards become filter 
    .flatMap { baz => 
      BowF(baz)
    }.map { baz => baz + 1 } // yield becomes map
  }
}

以上内容可以转换为

gpf.flatMap { _ => ccf }.map { _ => atbf }

所以你的理解力变得

 if(!empty($additional_features)){
          foreach($additional_features as $additional_feature){
            $data = [
               'name' => $additional_feature,
             ];
             if (!Feature::where('name', '=', $additional_feature)->exists()) {
                 $additional = Feature::firstOrCreate($data);
                 $additional_ids[] = $additional->id;
             }
             else{
               return redirect()->back()->withFlashMessage($additional_feature . ' exists!');
             }

          }
        }