Future flatMap example

gistfile1.scala

class HttpClient {
  def get(uri: URI): Future[String]
}

// return Future of next URI to get
def getUri(): Future[URI]

// return's available HttpClient from a pool
def getHttpClient(): Future[HttpClient]

// returns a Tuple of the URI and the client's result
getURI() flatMap { uri =>
  getHttpClient() flatMap { httpClient =>
    httpClient get uri map (result => (uri -> result))
  }
}

// The same as above, but as a for-comprehension
for {
  uri        <- getURI()
  httpClient <- getHttpClient()
  result     <- httpClient get uri
} yield (uri -> result)

// kinda Java
class HttpClient {
  def get(uri: URI): Future[String]
}

Future<URI> getUri() { ... }

Future<HttpClient> getHttpClient() { ... }

Mapper<String, Tuple2<URI, String>> formatResult(URI uri) {
  new Mapper<String, Tuple2<URI, String>>() {
    Tuple2<URI, String> apply(String str) {
      new Tuple2(uri, str)
    }
  }
}

Mapper<HttpClient, Future<Tuple2<URI, String>>> clientGetResult(URI uri) {
  new Mapper<String, Future<Tuple2<URI, String>>>() {
    Future<Tuple2<URI, String>> apply(HttpClient httpClient) {
      httpClient.get(uri).map(formatResult(uri))
    }
  }
}

Mapper<URI, Future<Tuple2<URI, String>>> uriGetResult() {
  new Mapper<URI, Future<Tuple2<URI, String>>>() {
    Future<Tuple2<URI, String>> apply(URI uri) {
      getHttpClient().flatMap(clientGetResult(uri))
    }
  }
}

getURI().flatMap(uriGetResult())

//without generics
Mapper formatResult(URI uri) {
  new Mapper() {
    Tuple2 apply(String str) {
      new Tuple2(uri, str)
    }
  }
}

Mapper clientGetResult(URI uri) {
  new Mapper() {
    Future apply(HttpClient httpClient) {
      httpClient.get(uri).map(formatResult(uri))
    }
  }
}

Mapper uriGetResult() {
  new Mapper() {
    Future apply(URI uri) {
      getHttpClient().flatMap(clientGetResult(uri))
    }
  }
}

getURI().flatMap(uriGetResult())