如何创建隐式字段transient?

Question

我想在apache Flink的AsyncFunction中设置doobie，但它需要一个隐式的读取输出实例。另一方面，我不能发送Read[Out]作为一个隐式参数，因为AsyncFunction需要是可序列化的，这个隐式值违反了这个规则:

package FlinkHelpers
import Configs.JdbConfig
import doobie.hikari._
import doobie._
import doobie.implicits._
import doobie.util.ExecutionContexts
import cats._
import cats.data._
import cats.effect.IO.asyncForIO
import cats.effect._
import cats.implicits._
import fs2.Stream
import cats.effect.unsafe.implicits.global
import org.apache.flink.runtime.concurrent.Executors
import org.apache.flink.streaming.api.scala.async.{AsyncFunction, ResultFuture}
import scala.concurrent.{ExecutionContext, Future}
import scala.util.Try
class AsyncDatabaseRequestOne[In,Out](configs:JdbConfig)(implicit r:Read[Out]) extends AsyncFunction[In,(In, Out)] {
lazy val transactor: Resource[IO, HikariTransactor[IO]] = {
for {
ce <- ExecutionContexts.fixedThreadPool[IO](32)
xa <- HikariTransactor.newHikariTransactor[IO](
"org.postgresql.Driver",
"jdbc:postgresql://localhost:5433/doobie",
"psql",
"110271",
ce
)
} yield xa
}
/** The context used for the future callbacks */
implicit lazy val executor: ExecutionContext = ExecutionContext.fromExecutor(Executors.directExecutor())
override def asyncInvoke(input: In, resultFuture: ResultFuture[(In, Out)]): Unit = {
val v2: IO[Out] = transactor.use[Out] { xa2: HikariTransactor[IO] => {
sql"select code,name,population,gnp from Out limit 1"
.query[Out] // Query0[String]
.unique // ConnectionIO[List[String]]
.transact(xa2) // IO[List[String]]
}
}
val future = v2.unsafeToFuture()
future.onSuccess({
case result: Out => resultFuture.complete(List((input, result)))
})
}
}

另一方面，scala不允许我使r字段过渡有人知道怎么解这个吗?

Answer 1

class AsyncDatabaseRequestOne[In,Out](configs:JdbConfig)(r:Read[Out])...中的r是一个构造函数参数，但是Scala也可以为它生成private[this]字段:

消除与父类的类字段同名的构造函数参数的歧义(answer)

尝试添加注释@transient

class AsyncDatabaseRequestOne[In,Out](configs:JdbConfig)(@transient private[this] implicit val r:Read[Out])...

或

class AsyncDatabaseRequestOne[In,Out](configs:JdbConfig)(@(transient @field) private[this] implicit val r:Read[Out])...

因为@transient已经被@field定义了

@field
final class transient extends scala.annotation.StaticAnnotation

我想在我们的情况下，@field元注释是不必要的。