OptionalT fromOptional和liftF在ScalaZ
问题描述:
从来就一直看着单子变压器的一些例子有Cats
,我试图重现那些Scalaz
OptionalT fromOptional和liftF在ScalaZ
在这里,我有一个为理解我第一次收到一个可选的,我flatMap与OptionalT
,第二个函数返回员工的未来。
这里我的代码
//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
}
此代码是从猫的版本,并在scalaz的OptionT.fromOption
包装一个选项不存在,我注意到,我可以做OptionT(Some(db.getCompany(companyName))
然后再编译,但现在的签名方法说,我返回一个可选的而不是未来。
怎么还可以使用OptionT.liftF
在ScalaZ
问候。
答
这些工作应作为替代品:
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]
然而,这将是件好事,这两种方法也OptionT
。您可以添加它们并打开拉取请求。
优秀的人,谢谢 – paul