如何在 Scala 中覆盖 `org.elasticsearch.client.FilterClient#doExecute()`？

Question

特别是 "org.elasticsearch" % "elasticsearch" % "2.4.x"（work 以后的版本 ElasticSearch 的其中 ActionRequest 不再采用参数类型，但我们还不能更新到那些！）。

我们试图覆盖的 Java 方法定义如下 (source):

protected <Request extends ActionRequest, Response extends ActionResponse, RequestBuilder extends ActionRequestBuilder<Request, Response, RequestBuilder>> void doExecute(Action<Request, Response, RequestBuilder> action, Request request, ActionListener<Response> listener) {
    in().execute(action, request, listener);
}

天真的尝试覆盖它...

import org.elasticsearch.action._
import org.elasticsearch.client.{Client, FilterClient}

class DemoFilterClient(underlyingClient: Client) extends FilterClient(underlyingClient) {
  override def doExecute[
    Request <: ActionRequest[_],
    Response <: ActionResponse,
    RequestBuilder <: ActionRequestBuilder[Request, Response, RequestBuilder]
  ](
    action: Action[Request, Response, RequestBuilder],
    request: Request,
    listener: ActionListener[Response]
  ) = super.doExecute(action, request, listener)
}

...fails 在我们尝试过的所有 Scala 版本中（2.11.11、2.11.12 和 2.12.4）：

[info] Compiling 1 Scala source to /home/roberto/development/elasticsearch-scala-client-test/target/scala-2.11/classes ...
[error] /home/roberto/development/elasticsearch-scala-client-test/src/main/scala/com/gu/DemoFilterClient.scala:7:101: type arguments [Request,Response,RequestBuilder] do not conform to class ActionRequestBuilder's type parameter bounds [Request <: org.elasticsearch.action.ActionRequest[_ <: org.elasticsearch.action.ActionRequest[_ <: org.elasticsearch.action.ActionRequest[_ <: AnyRef]]],Response <: org.elasticsearch.action.ActionResponse,RequestBuilder <: org.elasticsearch.action.ActionRequestBuilder[Request,Response,RequestBuilder]]
[error]   override def doExecute[Request <: ActionRequest[_], Response <: ActionResponse, RequestBuilder <: ActionRequestBuilder[Request, Response, RequestBuilder]](action: Action[Request, Response, RequestBuilder], request: Request, listener: ActionListener[Response]) = super.doExecute(action, request, listener)
[error]                                                                                                     ^
[error] one error found

为了更清楚地列出编译器错误：

type arguments
[Request,Response,RequestBuilder]
do not conform to class ActionRequestBuilder's type parameter bounds
[
  Request <: 
    org.elasticsearch.action.ActionRequest[_ <: 
      org.elasticsearch.action.ActionRequest[_ <: 
        org.elasticsearch.action.ActionRequest[_ <: AnyRef]]],
  Response <: org.elasticsearch.action.ActionResponse,
  RequestBuilder <: org.elasticsearch.action.ActionRequestBuilder[Request,Response,RequestBuilder]
]

请注意 Request 类型的惊人递归声明！

示例 sbt 项目可在 https://github.com/guardian/elasticsearch-scala-client-test

获得

Answer 1

我已经运行遇到过这种 F 有界多态性与原始 Java 类型之前的情况，如果我没记错的话，这样的事情应该有效（至少它在您的示例项目中编译):

package com.gu

import org.elasticsearch.action._
import org.elasticsearch.client.{Client, FilterClient}

class DemoFilterClient(underlyingClient: Client)
    extends FilterClient(underlyingClient) {

  type AR[x <: ActionRequest[x]] = ActionRequest[x]

  override def doExecute[
    Request <: AR[_],
    Response <: ActionResponse,
    RequestBuilder <: ActionRequestBuilder[Request, Response, RequestBuilder]
  ](
    action: Action[Request, Response, RequestBuilder],
    request: Request,
    listener: ActionListener[Response]
  ) = super.doExecute(action, request, listener)
}

似乎也可以使用 forSome 内联执行此操作，但我刚才尝试的 none 迭代已经奏效了。

如何在 Scala 中覆盖 `org.elasticsearch.client.FilterClient#doExecute()`？

How to override `org.elasticsearch.client.FilterClient#doExecute()` in Scala?

scala

scala-java-interop

elasticsearch-2.4