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Add or combinator to Validated #1448

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Nov 15, 2016
Merged

Add or combinator to Validated #1448

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e66f7a1
Added findValid method on Validated that accumulates errors. Closes #…
mgzuber Nov 2, 2016
3102154
Added tests for orElse and findValid on Validated
mgzuber Nov 4, 2016
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14 changes: 14 additions & 0 deletions core/src/main/scala/cats/data/Validated.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -44,13 +44,27 @@ sealed abstract class Validated[+E, +A] extends Product with Serializable {

/**
* Return this if it is Valid, or else fall back to the given default.
* The functionality is similar to that of [[findValid]] except for failure accumulation,
* where here only the error on the right is preserved and the error on the left is ignored.
*/
def orElse[EE, AA >: A](default: => Validated[EE, AA]): Validated[EE, AA] =
this match {
case v @ Valid(_) => v
case Invalid(_) => default
}

/**
* If `this` is valid return `this`, otherwise if `that` is valid return `that`, otherwise combine the failures.
* This is similar to [[orElse]] except that here failures are accumulated.
*/
def findValid[EE >: E, AA >: A](that: => Validated[EE, AA])(implicit EE: Semigroup[EE]): Validated[EE, AA] = this match {
case v @ Valid(_) => v
case Invalid(e) => that match {
case v @ Valid(_) => v
case Invalid(ee) => Invalid(EE.combine(e, ee))
}
}

/**
* Converts the value to an Either[E, A]
*/
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19 changes: 19 additions & 0 deletions tests/src/test/scala/cats/tests/ValidatedTests.scala
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Expand Up @@ -114,6 +114,25 @@ class ValidatedTests extends CatsSuite {
}
}

test("findValid accumulates failures") {
forAll { (v: Validated[String, Int], u: Validated[String, Int]) =>
v findValid u shouldEqual { (v, u) match {
case (vv @ Valid(_), _) => vv
case (_, uu @ Valid(_)) => uu
case (Invalid(s1), Invalid(s2)) => Invalid(s1 ++ s2)
}}
}
}

test("orElse ignores left failure") {
forAll { (v: Validated[String, Int], u: Validated[String, Int]) =>
v orElse u shouldEqual { (v, u) match {
case (vv @ Valid(_), _) => vv
case (_, uu) => uu
}}
}
}

test("valueOr consistent with swap then map then merge") {
forAll { (v: Validated[String, Int], f: String => Int) =>
v.valueOr(f) should === (v.swap.map(f).merge)
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