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November 5, 2014 08:12
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Example showing Scalactic's Validation used to accumulate errors with the "when" combinator
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| scala> import org.scalactic._ | |
| import org.scalactic._ | |
| // A Validation is either a Pass or a Fail. A Validation is like an | |
| // Option with the reverse attitude: Pass is like None, it contains no | |
| // value and just means the value being validated is OK as is. Fail is | |
| // like Some, it holds an error value describing the validation failure. | |
| scala> def isPositive(i: Int): Validation[ErrorMessage] = | |
| | if (i > 0) Pass else Fail(s"$i was not positive") | |
| isPositive: (i: Int)org.scalactic.Validation[org.scalactic.ErrorMessage] | |
| scala> isPositive(3) | |
| res0: org.scalactic.Validation[org.scalactic.ErrorMessage] = Pass | |
| scala> isPositive(-3) | |
| res1: org.scalactic.Validation[org.scalactic.ErrorMessage] = Fail(-3 was not positive) | |
| // Validations can be used with when to accumulate errors (including in for expressions) | |
| scala> def parseInt(input: String): Int Or One[ErrorMessage] = { | |
| | try Good(input.trim.toInt) | |
| | catch { | |
| | case _: NumberFormatException => Bad(One(s"$input was not an integer")) | |
| | } | |
| | } | |
| parseInt: (input: String)org.scalactic.Or[Int,org.scalactic.One[org.scalactic.ErrorMessage]] | |
| scala> import Accumulation._ | |
| import Accumulation._ | |
| scala> parseInt("three") when isPositive | |
| res2: org.scalactic.Or[Int,org.scalactic.Every[org.scalactic.ErrorMessage]] = Bad(One(three was not an integer)) | |
| scala> parseInt("3") when isPositive | |
| res3: org.scalactic.Or[Int,org.scalactic.Every[org.scalactic.ErrorMessage]] = Good(3) | |
| scala> parseInt("-3") when isPositive | |
| res4: org.scalactic.Or[Int,org.scalactic.Every[org.scalactic.ErrorMessage]] = Bad(One(-3 was not positive)) | |
| // You can use when to accumulate errors from multiple validations | |
| scala> def isRound(i: Int): Validation[ErrorMessage] = | |
| | if (i % 10 == 0) Pass else Fail(s"$i was not evenly divisible by 10") | |
| isRound: (i: Int)org.scalactic.Validation[org.scalactic.ErrorMessage] | |
| // "30" passes both isPositive and isRound validations | |
| scala> parseInt("30") when (isPositive, isRound) | |
| res5: org.scalactic.Or[Int,org.scalactic.Every[org.scalactic.ErrorMessage]] = Good(30) | |
| // "3" fails the isRound validation | |
| scala> parseInt("3") when (isPositive, isRound) | |
| res6: org.scalactic.Or[Int,org.scalactic.Every[org.scalactic.ErrorMessage]] = Bad(One(3 was not evenly divisible by 10)) | |
| // "-30" fails the isPositive validation | |
| scala> parseInt("-30") when (isPositive, isRound) | |
| res7: org.scalactic.Or[Int,org.scalactic.Every[org.scalactic.ErrorMessage]] = Bad(One(-30 was not positive)) | |
| // "-3" fails both validations, so two error messages appear in the result | |
| scala> parseInt("-3") when (isPositive, isRound) | |
| res8: org.scalactic.Or[Int,org.scalactic.Every[org.scalactic.ErrorMessage]] = | |
| Bad(Many(-3 was not positive, -3 was not evenly divisible by 10)) |
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