scala：将错误添加到错误列表的惯用和功能方法

发布时间：2020-12-16 10:08:22 所属栏目：安全来源：网络整理

导读：我有以下验证方法： def validate(wine: Wine): List[Error] = { var errors = List[Error]() if (Validate.isEmptyWord(wine.name)) { errors ::= ValidationError("name","Name not specified") } else { if (isDuplicate(wine,"name")) { errors ::= Vali

我有以下验证方法：

def validate(wine: Wine): List[Error] = {

  var errors = List[Error]()

  if (Validate.isEmptyWord(wine.name)) {
    errors ::= ValidationError("name","Name not specified")
  } else {
    if (isDuplicate(wine,"name")) {
      errors ::= ValidationError("name","There already exists a wine with the name '%s'".format(wine.name))
    }
  }

  if (Validate.isEmptyWord(wine.grapes)) {
    errors ::= ValidationError("grapes","Grapes not specified")
  }

  if (Validate.isEmptyWord(wine.country)) {
    errors ::= ValidationError("country","Country not specified")
  }

  // more stuff like this and finnally
  errors.reverse
}

你明白了

你将如何修改它以避免var List [Error]并使其更具功能性？

解决方法

Scalaz提供了一个Validation类,可以很容易地解决这类问题.有一个更详细的例子说明如何在 this Stack Overflow answer中使用验证,但我也会在这里给出一个草图,以说明它在你的情况下如何工作.我将假设以下设置：

case class Wine(name: String,grapes: String,country: String)
case class ValidationError(name: String,msg: String)

现在我们可以编写几种验证方法(注意我使用的是Scalaz 7)：

import scalaz._,Scalaz._

def checkNonempty(v: String,name: String,msg: String) =
  if (v.nonEmpty) v.successNel else ValidationError(name,msg).failNel

def checkDuplicate(v: String,msg: String) =
  if (true) v.successNel else ValidationError(name,msg).failNel

当然,您应该在最后一行添加自己的复制检查.然后我们可以将它们包装在一起：

def createWine(name: String,grape: String,country: String) = (
  checkNonempty(name,"name","Name not specified").flatMap(_ =>
    checkDuplicate(name,"There already exists a wine with the name '%s'".format(name)
    )
  ) |@|
  checkNonempty(grape,"grape","Grape not specified") |@|
  checkNonempty(country,"country","Country not specified")
)(Wine.apply)

现在,如果我们写这样的东西：

val result: ValidationNEL[ValidationError,Wine] = createWine(
  "Whatever Estates","Whatever Grape","U.S."
)

我们将获得成功价值：

Success(Wine(Whatever Estates,Whatever Grape,U.S.))

但是如果我们给它无效的输入：

val result: ValidationNEL[ValidationError,Wine] = createWine(
  "","Some Grape",""
)

我们将获得累积错误的列表：

Failure(
  NonEmptyList(
    ValidationError(name,Name not specified),ValidationError(country,Country not specified)
  )
)

当然,你也可以推出自己的验证逻辑,但是如果你做了很多这样的事情,使用像Scalaz这样的库可能是值得的.

（编辑：李大同）

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