Scala-Cats：验证地图的条目

Question

假设我有：

val m: Map[String, Int] = Map("one" -> 1, "five" -> 5, "six" -> 6, "nine" -> 9)

我有两个功能：

def isNotDivisibleByTwo(i: Int): ValidatedNec[String, Int] = Validated.condNec(i%2!=0, i, s"$i is divisible by 2.")
def isNotDivisibleByThree(i: Int): ValidatedNec[String, Int] = Validated.condNec(i%3!=0, i, s"$i is divisible by 3.")

我想要一个函数，它能给我：

def sanitize(m: Map[String, Int]):Map[String, Validated[NonEmptyList[String], Int]] = ???

即，它应该返回满足上述两个函数的所有数字，以及所有故障数字及其相关故障的映射。
例如，对于给定的列表 m，我想得到：

val result = Map(
"one" -> Valid(1),
"five -> Valid(5),
"nine" -> Invalid(NonEmptyList("9 is dividible by 3")),
"six" -> Invalid(NonEmptyList("6 is dividible by 2", "6 is dividible by 3"))
)

这是我目前拥有的：

import cats.data._
val m: Map[String, Int] = Map("one" -> 1, "five" -> 5, "six" -> 6, "nine" -> 9)
def isNotDivisibleByTwo(i: Int): ValidatedNec[String, Unit] = Validated.condNec(i%2!=0, (), s"$i is divisible by 2.")
def isNotDivisibleByThree(i: Int): ValidatedNec[String, Unit] = Validated.condNec(i%3!=0, (), s"$i is divisible by 3.")

def sanitize(m: Map[String, Int]): Map[String, Validated[NonEmptyChain[String], Int]] = {
m.mapValues{
i =>
isNotDivisibleByTwo(i).product(
isNotDivisibleByThree(i)
).map(_ => i)
}
}

但是，我对"撰写"验证的方式不满意。

我怎样才能以最猫的方式做到这一点？

Answer 1

你们离得太近了。
请记住，组合多个验证的正确方法是使用Applicative语法。

import cats.data.{Validated, ValidatedNec}
import cats.syntax.apply._
type ErrorsOr[A] = ValidatedNec[String, A]
def isNotDivisibleByTwo(i: Int): ErrorsOr[Int] =
Validated.condNec((i % 2) != 0, i, s"$i is divisible by 2.")
def isNotDivisibleByThree(i: Int): ErrorsOr[Int] =
Validated.condNec((i % 3) != 0, i, s"$i is divisible by 3.")
val map: Map[String, Int] = Map("one" -> 1, "five" -> 5, "six" -> 6, "nine" -> 9)
def sanitize(m: Map[String, Int]): Map[String, ErrorsOr[Int]] =
m.view.mapValues { i =>
(
isNotDivisibleByTwo(i),
isNotDivisibleByThree(i)
).tupled.map(_ => i)
}.toMap
sanitize(map)
// res: Map[String, ErrorsOr[Int]] = Map(
//   "one" -> Valid(1),
//   "five" -> Valid(5),
//   "six" -> Invalid(Append(Singleton("6 is divisible by 2."), Singleton("6 is divisible by 3."))),
//   "nine" -> Invalid(Singleton("9 is divisible by 3."))
// )

但是，您可以使代码更加通用，以使用任意数量的验证。通过使用traverse.
(在这种情况下，您不需要任何语法导入(。

import cats.data.NonEmptyList
val validations: NonEmptyList[Int => ErrorsOr[Int]] = NonEmptyList.of(isNotDivisibleByTwo, isNotDivisibleByThree)
def sanitize[K, V](map: Map[K, V])
(validations: NonEmptyList[V => ErrorsOr[V]]): Map[K, ErrorsOr[V]] =
map.view.mapValues(i => validations.traverse(f => f(i)).map(_ => i)).toMap
sanitize(map)(validations)
// res: Map[String, ErrorsOr[Int]] = Map(
//   "one" -> Valid(1),
//   "five" -> Valid(5),
//   "six" -> Invalid(Append(Singleton("6 is divisible by 2."), Singleton("6 is divisible by 3."))),
//   "nine" -> Invalid(Singleton("9 is divisible by 3."))
// )

---

我之所以使用.view.mapValues(...).toMap是因为在Scala 2.13上mapValues已被弃用。