Scala monads - “值映射不是”错误的成员

Question

我创建了一个简单的trait和服务：

@finalAlg
@autoFunctorK(true)
trait BettingService[F[_]] {    
  def put(bet: Bet): F[Bet]
}

class BettingServiceMock[F[_] : Async] extends BettingService[F] {
  override def put(bet: Bet): F[Bet] = {
    val id = randomUUID().toString
    for {
      created <- Bet(BetId(id), bet.stake, bet.name)
    } yield created
  }
}

Bet和BetId是case classes：

case class Bet(betId: BetId, stake: BigDecimal, name: String)

case class BetId(betId: String) extends AnyVal

当我运行这个程序时，我收到一个错误：Error:(12, 21) value map is not a member of model.Bet <- Bet(BetId(id), bet.stake, bet.name)这对我来说很奇怪 - 为什么我不能从for-comprehension返回好的类型？这个想法是返回与参数给定的相同对象，但具有随机id。

我想也许我需要新的Bet类的实例，但是我不能像我想的那样将它作为F[_]返回。

Answer 1

Bet(BetId(id), bet.stake, bet.name)是Bet类型，但预期类型是F[Bet]。

尝试

import cats.syntax.functor._

for {
  created <- Applicative[F].pure(Bet(BetId(id), bet.stake, bet.name))
} yield created

要么

import cats.syntax.functor._
import cats.syntax.applicative._

for {
  created <- Bet(BetId(id), bet.stake, bet.name).pure
} yield created

要么

Applicative[F].pure(Bet(BetId(id), bet.stake, bet.name))

要么

import cats.syntax.applicative._

Bet(BetId(id), bet.stake, bet.name).pure