OptionalT fromOptional 和 ScalaZ 中的 liftF

Question

我一直在用 Cats 观看一些 monads 转换器的例子，我试图在 Scalaz

中重现这些例子

这里我有一个理解，我首先收到一个可选的，我用 OptionalT 进行 flatMap，第二个函数 return 是员工的未来。

这是我的代码

  //Attributes for this example
  sealed trait Employee {
    val id: String
  }

  final case class EmployeeWithoutDetails(id: String) extends Employee

  final case class EmployeeWithDetails(id: String, name: String, city: String, age: Int) extends Employee

  case class Company(companyName: String, employees: List[EmployeeWithoutDetails])

  trait HybridDBOps {
    protected def getDetails(employeeId: String): Future[EmployeeWithDetails]

    protected def getCompany(companyName: String): Option[Company]
  }

  class DbHybrid extends HybridDBOps {
    override def getDetails(employeeId: String): Future[EmployeeWithDetails] = Future {
      EmployeeWithDetails("1", "name", "city", 36)
    }

    override def getCompany(companyName: String): Option[Company] = Some(Company(companyName, List(EmployeeWithoutDetails("1"))))
  }

  def getEmployeeAgeScalaZHybrid(employeeId: String, companyName: String): Future[Option[Int]] = {
    val db = new DbHybrid
    val eventualOption = (for {
      company <- OptionT.fromOption(db.getCompany(companyName)) --> Wont compile
      if company.employees map (_.id) contains employeeId
      details <- OptionT.liftF(db.getDetails(employeeId)) --> Wont compile
    } yield details.age).run
    eventualOption
  }

此代码来自 cats 版本，在 scalaz 中 OptionT.fromOption 包装选项不存在，我注意到我可以执行 OptionT(Some(db.getCompany(companyName)) 然后编译，但现在方法的签名说我 return 使用可选而不是未来。

还有如何在ScalaZ

中使用OptionT.liftF

这里是完整的例子https://github.com/politrons/reactiveScala/blob/master/scala_features/src/main/scala/app/impl/scalaz/MonadTransformer.scala

此致。

Answer 1

这些应该可以作为替代品：

import scalaz.std.future._
import scalaz.syntax.monad._

// instead of OptionT.fromOption(db.getCompany(companyName))
OptionT(db.getCompany(companyName).pure[Future])

// instead of OptionT.liftF(db.getDetails(employeeId))
db.getDetails(employeeId).liftM[OptionT]

不过，最好在 OptionT 上同时使用这两种方法。您可以添加它们并打开拉取请求。

OptionalT fromOptional 和 ScalaZ 中的 liftF

OptionalT fromOptional and liftF in ScalaZ

scala

scalaz

scala-cats