我与猫初学者。我有一个经验证的猫一个错误。我用一个列表蓄电池这样的:
case class Type(
name: String,
pattern: String,
primitiveType: PrimitiveType = PrimitiveType.string,
sample: Option[String] = None,
comment: Option[String] = None,
stat: Option[Stat] = None
) {
type ValidationResult[A] = Validated[List[String], A]
def checkValidity(): ValidationResult[Boolean] = {
val errorList: mutable.MutableList[String] = mutable.MutableList.empty
val patternIsValid = Try {
primitiveType match {
case PrimitiveType.struct =>
case PrimitiveType.date =>
new SimpleDateFormat(pattern)
case PrimitiveType.timestamp =>
pattern match {
case "epoch_second" | "epoch_milli" =>
case _ if PrimitiveType.formatters.keys.toList.contains(pattern) =>
case _ =>
DateTimeFormatter.ofPattern(pattern)
}
case _ =>
Pattern.compile(pattern)
}
}
if (patternIsValid.isFailure)
errorList += s"Invalid Pattern $pattern in type $name"
val ok = sample.forall(this.matches)
if (!ok)
errorList += s"Sample $sample does not match pattern $pattern in type $name"
if (errorList.nonEmpty)
Invalid(errorList.toList)
else
Valid(true)
}
}
当我使用此功能与我的情况类类型:
case class Types(types: List[Type]) {
type ValidationResult[A] = Validated[List[String], A]
def checkValidity(): ValidationResult[Boolean] = {
val typeNames = types.map(_.name)
val dup: ValidationResult[Boolean] =
duplicates(typeNames, s"%s is defined %d times. A type can only be defined once.")
(dup,types.map(_.checkValidity()).sequence).mapN((_,_) => true)
}
}
我有这样的错误
Error:(29, 39) Cannot prove that cats.data.Validated[List[String],Boolean] <:< G[A].
(dup,types.map(_.checkValidity()).sequence: _*).mapN((_,_) => true)
你能不能帮我解决这个问题?
谢谢你的帮助。
很多年前,我写了一个关于潜在问题long blog post你正在运行到这里,如果你有兴趣在历史上还是一些老的解决方法,但幸运的是,现在的解决方案是很容易(假设你在斯卡拉2.11或2.12) :只需添加-Ypartial-unification
到您的Scala编译器选项。如果您正在使用SBT,例如,可能是这样的:
scalacOptions += "-Ypartial-unification"
就大功告成了。
如果由于某种原因,你不能添加编译器选项,你必须明确地提供某种类型的参数。这里有一个快速简化版本:
import cats.data.Validated, cats.implicits._
case class Foo(i: Int) {
type ValidationResult[A] = Validated[List[String], A]
def check: ValidationResult[Boolean] =
if (i < 0) Validated.invalid(List("bad")) else Validated.valid(true)
}
case class Foos(values: List[Foo]) {
type ValidationResult[A] = Validated[List[String], A]
def dup: ValidationResult[Unit] = Validated.valid(())
def check: ValidationResult[Boolean] =
(dup, values.map(_.check).sequence).mapN((_, _) => true)
}
这将失败,你看到的错误(假设你没有添加-Ypartial-unification
):
<console>:22: error: Cannot prove that cats.data.Validated[List[String],Boolean] <:< G[A].
(dup, values.map(_.check).sequence).mapN((_, _) => true)
^
要解决它,你可以写:
case class Foos(values: List[Foo]) {
type ValidationResult[A] = Validated[List[String], A]
def dup: ValidationResult[Unit] = Validated.valid(())
def check: ValidationResult[Boolean] =
(dup, values.map(_.check).sequence[ValidationResult, Boolean]).mapN((_, _) => true)
}
我想你也很可能只是移动式别名包级别,但我不是100%肯定没有,我不上进检查,对不起。
一个注脚:你有map
然后sequence
,您可以通过使用traverse
,而不是使事情更快一点任何时候:
def check: ValidationResult[Boolean] =
(dup, values.traverse[ValidationResult, Boolean](_.check)).mapN((_, _) => true)
同样,你可以删除该类型的参数,并让类型推断推测出来,如果你有-Ypartial-unification
启用。