Trait

org.scalactic

Validation

Related Doc: package scalactic

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sealed trait Validation[+E] extends Product with Serializable

Represents the result of a validation, either the object Pass if the validation succeeded, else an instance of Fail containing an error value describing the validation failure.

Validations are used to filter Ors in for expressions or filter method calls. For example, consider these methods:

import org.scalactic._

def isRound(i: Int): Validation[ErrorMessage] =
  if (i % 10 == 0) Pass else Fail(i + " was not a round number")

def isDivBy3(i: Int): Validation[ErrorMessage] =
  if (i % 3 == 0) Pass else Fail(i + " was not divisible by 3")

Because isRound and isDivBy3 take an Int and return a Validation[ErrorMessage], you can use them in filters in for expressions involving Ors of type Int Or ErrorMessage. Here's an example:

for (i <- Good(3) if isRound(i) && isDivBy3(i)) yield i
// Result: Bad(3 was not a round number)

Validations can also be used to accumulate error using when, a method that's made available by trait Accumulation on accumualting Ors (Ors whose Bad type is an Every[T]). Here are some examples:

import Accumulation._

for (i <- Good(3) when (isRound, isDivBy3)) yield i
// Result: Bad(One(3 was not a round number))

for (i <- Good(4) when (isRound, isDivBy3)) yield i
// Result: Bad(Many(4 was not a round number, 4 was not divisible by 3))

Note: You can think of Validation as an “Option with attitude,” where Pass is a None that indicates validation success and Fail is a Some whose value describes the validation failure.

E

the type of error value describing a validation failure for this Validation

Source
Validation.scala
Linear Supertypes
Serializable, Serializable, Product, Equals, AnyRef, Any
Known Subclasses
Fail, Pass
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  1. Validation
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Abstract Value Members

  1. abstract def &&[F >: E](other: ⇒ Validation[F]): Validation[F]

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    Ands this Validation with another, passed, Validation.

    Ands this Validation with another, passed, Validation.

    The result of and-ing two Validations is:

    ExpressionResult
    Pass && PassPass
    Pass && Fail(right)Fail(right)
    Fail(left) && PassFail(left)
    Fail(left) && Fail(right)Fail(left)

    As you can see in the above table, no attempt is made by && to accumulate errors, which in turn means that no constraint is placed on the E type (it need not be an Every). Instead, && short circuits and returns the first Fail it encounters. This makes it useful in filters in for expressions involving Ors. Here's an example:

    import org.scalactic._

def isRound(i: Int): Validation[ErrorMessage] =
  if (i % 10 != 0) Fail(i + " was not a round number") else Pass

def isDivBy3(i: Int): Validation[ErrorMessage] =
  if (i % 3 != 0) Fail(i + " was not divisible by 3") else Pass

for (i <- Good(3) if isRound(i) && isDivBy3(i)) yield i
// Result: Bad(3 was not a round number)

    other

    the other validation to and with this one

    returns

    the result of anding this Validation with the other, passed, Validation

  2. abstract def canEqual(that: Any): Boolean

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    Definition Classes
    Equals

  3. abstract def productArity: Int

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    Definition Classes
    Product

  4. abstract def productElement(n: Int): Any

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    Definition Classes
    Product

Concrete Value Members

  1. final def !=(arg0: Any): Boolean

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    AnyRef → Any

  2. final def ##(): Int

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    AnyRef → Any

  3. final def ==(arg0: Any): Boolean

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    AnyRef → Any

  4. final def asInstanceOf[T0]: T0

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    Any

  5. def clone(): AnyRef

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    protected[java.lang]
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    AnyRef
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    @throws( ... )

  6. final def eq(arg0: AnyRef): Boolean

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    AnyRef

  7. def equals(arg0: Any): Boolean

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    AnyRef → Any

  8. def finalize(): Unit

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    protected[java.lang]
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    AnyRef
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    @throws( classOf[java.lang.Throwable] )

  9. final def getClass(): Class[_]

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  10. def hashCode(): Int

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  11. final def isInstanceOf[T0]: Boolean

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    Any

  12. final def ne(arg0: AnyRef): Boolean

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    AnyRef

  13. final def notify(): Unit

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    AnyRef

  14. final def notifyAll(): Unit

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    Definition Classes
    AnyRef

  15. def productIterator: Iterator[Any]

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    Definition Classes
    Product

  16. def productPrefix: String

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    Definition Classes
    Product

  17. final def synchronized[T0](arg0: ⇒ T0): T0

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    AnyRef

  18. def toString(): String

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  19. final def wait(): Unit

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    @throws( ... )

  20. final def wait(arg0: Long, arg1: Int): Unit

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  21. final def wait(arg0: Long): Unit

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