Merge pull request #984 from markus1189/validated-ensure

Add Validated.ensure
typelevel · May 9, 2016 · 19d0de0 · 19d0de0
2 parents 40a1211 + e3eb1d0
commit 19d0de0
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diff --git a/core/src/main/scala/cats/data/Validated.scala b/core/src/main/scala/cats/data/Validated.scala
@@ -202,6 +202,20 @@ sealed abstract class Validated[+E, +A] extends Product with Serializable {
     case Valid(a) => Invalid(a)
     case Invalid(e) => Valid(e)
   }
+
+  /**
+   * Ensure that a successful result passes the given predicate,
+   * falling back to an Invalid of `onFailure` if the predicate
+   * returns false.
+   *
+   * For example:
+   * {{{
+   * scala> Validated.valid("").ensure(new IllegalArgumentException("Must not be empty"))(_.nonEmpty)
+   * res0: Validated[IllegalArgumentException,String] = Invalid(java.lang.IllegalArgumentException: Must not be empty)
+   * }}}
+   */
+  def ensure[EE >: E](onFailure: => EE)(f: A => Boolean): Validated[EE, A] =
+    fold(_ => this, a => if (f(a)) this else Validated.invalid(onFailure))
 }
 
 object Validated extends ValidatedInstances with ValidatedFunctions{

diff --git a/tests/src/test/scala/cats/tests/ValidatedTests.scala b/tests/src/test/scala/cats/tests/ValidatedTests.scala
@@ -195,4 +195,20 @@ class ValidatedTests extends CatsSuite {
     val z = x.map2(y)((i, b) => if (b) i + 1 else i)
     z should === (NonEmptyList("error 1", "error 2").invalid[Int])
   }
+
+  test("ensure on Invalid is identity") {
+    forAll { (x: Validated[Int,String], i: Int, p: String => Boolean) =>
+      if (x.isInvalid) {
+        x.ensure(i)(p) should === (x)
+      }
+    }
+  }
+
+  test("ensure should fail if predicate not satisfied") {
+    forAll { (x: Validated[String, Int], s: String, p: Int => Boolean) =>
+      if (x.exists(!p(_))) {
+        x.ensure(s)(p) should === (Validated.invalid(s))
+      }
+    }
+  }
 }