SCALA-45 Partial Functions

core-scala/src/main/scala/com/baeldung/scala/partialfunctions/SquareRoot.scala

@@ -0,0 +1,12 @@
+package com.baeldung.scala.partialfunctions
+
+object SquareRoot {
+  val squareRoot = new PartialFunction[Double, Double] {
+    def apply(x: Double) = Math.sqrt(x)
+    def isDefinedAt(x: Double) = x >= 0
+  }
+
+  val squareRootImplicit: PartialFunction[Double, Double] = {
+    case x if x >= 0 => Math.sqrt(x)
+  }
+}

core-scala/src/main/scala/com/baeldung/scala/partialfunctions/SwapIntegerSign.scala

@@ -0,0 +1,20 @@
+package com.baeldung.scala.partialfunctions
+
+object SwapIntegerSign {
+
+  private val negativeOrZeroToPositive: PartialFunction[Int, Int] = {
+    case x if x <= 0 => Math.abs(x)
+  }
+
+  private val positiveToNegative: PartialFunction[Int, Int] = {
+    case x if x > 0 => -1 * x
+  }
+
+  val swapSign: PartialFunction[Int, Int] = {
+    positiveToNegative orElse negativeOrZeroToPositive
+  }
+
+  val printIfPositive: PartialFunction[Int, Unit] = {
+    case x if x > 0 => println(s"$x is positive!")
+  }
+}

core-scala/src/test/scala/com/baeldung/scala/partialfunctions/SquareRootUnitTest.scala

@@ -0,0 +1,24 @@
+package com.baeldung.scala.partialfunctions
+
+import org.scalatest.FlatSpec
+
+class SquareRootUnitTest extends FlatSpec {
+
+  "SquareRoot" should "return the correct value for positive double" in {
+    assert(SquareRoot.squareRoot(4.0) == 2.0)
+  }
+
+  it should "return NaN for a negative double" in {
+    assert(SquareRoot.squareRoot(-4.0).equals(Double.NaN))
+  }
+
+  "SquareRootImplicit" should "return the correct value for a positive double" in {
+    assert(SquareRoot.squareRootImplicit(4.0) == 2.0)
+  }
+
+  it should "throw a 'scala.MatchError' exception" in {
+    assertThrows[scala.MatchError] {
+      SquareRoot.squareRootImplicit(-4.0)
+    }
+  }
+}

core-scala/src/test/scala/com/baeldung/scala/partialfunctions/SwapIntegerSignUnitTest.scala

@@ -0,0 +1,38 @@
+package com.baeldung.scala.partialfunctions
+
+import org.scalatest.FlatSpec
+
+class SwapIntegerSignUnitTest extends FlatSpec {
+
+  "swapSign" should "return a positive number when a negative is given" in {
+    assert(SwapIntegerSign.swapSign(-3) == 3)
+  }
+
+  it should "return a negative number when a positive is given" in {
+    assert(SwapIntegerSign.swapSign(3) == -3)
+  }
+
+  "printIfPositive" should "print a positive number" in {
+    assert(SwapIntegerSign.printIfPositive(3).getClass == classOf[Unit])
+  }
+
+  it should "throw a 'scala.MatchError' exception given a negative number" in {
+    assertThrows[scala.MatchError] {
+      SwapIntegerSign.printIfPositive(-3)
+    }
+  }
+
+  "swapSign andThen printIfPositive" should "chain and print a positive number" in {
+    assert(
+      (SwapIntegerSign.swapSign andThen SwapIntegerSign.printIfPositive)(-1).getClass == classOf[
+        Unit
+      ]
+    )
+  }
+
+  it should "chain and throw a 'scala.MatchError' exception given a negative number" in {
+    assertThrows[scala.MatchError] {
+      (SwapIntegerSign.swapSign andThen SwapIntegerSign.printIfPositive)(1)
+    }
+  }
+}