Merge pull request #223 from robstoll/feature/mapFirst-second

Pair.mapFirst/mapSecond

README.md

@@ -20,6 +20,7 @@ in the stdlib such as:
 - blankToNull
 - isNotNullAndNotEmpty
 - identity
+- Pair.mapFirst/Second
 
 and more, see the [Documentation](https://robstoll.github.io/kbox/kdoc/) for a full list.
 

src/commonMain/kotlin/ch/tutteli/kbox/mapPair.kt

@@ -0,0 +1,21 @@
+package ch.tutteli.kbox
+
+/**
+ * Maps the first element of this [Pair] with the given function [transform].
+ *
+ * @return A new pair with the result of the transformation as first and the existing second as second element.
+ *
+ * @since 1.3.0
+ */
+fun <FirstT, SecondT, R> Pair<FirstT, SecondT>.mapFirst(transform: (FirstT) -> R): Pair<R, SecondT> =
+    Pair(transform(first), second)
+
+/**
+ * Maps the second element of this [Pair] with the given function [transform].
+ *
+ * @return A new pair with the existing first element as first and the result of the transformation as second element.
+ *
+ * @since 1.3.0
+ */
+fun <FirstT, SecondT, R> Pair<FirstT, SecondT>.mapSecond(transform: (SecondT) -> R): Pair<FirstT, R> =
+    Pair(first, transform(second))

src/commonTest/kotlin/ch/tutteli/kbox/MapPairTest.kt

@@ -0,0 +1,38 @@
+package ch.tutteli.kbox
+
+import ch.tutteli.atrium.api.fluent.en_GB.first
+import ch.tutteli.atrium.api.fluent.en_GB.second
+import ch.tutteli.atrium.api.fluent.en_GB.toBeTheInstance
+import ch.tutteli.atrium.api.fluent.en_GB.toEqual
+import ch.tutteli.atrium.api.verbs.expect
+import kotlin.test.Test
+
+class MapTupleTest {
+    @Test
+    fun mapFirst_identity_returns_equal_pair() {
+        expect(Pair(1, "hello").mapFirst(::identity)).toEqual(Pair(1, "hello"))
+    }
+
+    @Test
+    fun mapFirst_returns_transformation_does_not_touch_second_element() {
+        val obj = listOf('h', 'e', 'l', 'l', 'o')
+        expect(Pair(1, obj).mapFirst { it + 1 }) {
+            toEqual(Pair(2, obj))
+            second.toBeTheInstance(obj)
+        }
+    }
+
+    @Test
+    fun mapSecond_identity_returns_equal_pair() {
+        expect(Pair(1, "hello").mapSecond(::identity)).toEqual(Pair(1, "hello"))
+    }
+
+    @Test
+    fun mapSecond_returns_transformation_does_not_touch_first_element() {
+        val obj = listOf('h', 'e', 'l', 'l', 'o')
+        expect(Pair(obj, 1).mapSecond { it + 1 }) {
+            toEqual(Pair(obj, 2))
+            first.toBeTheInstance(obj)
+        }
+    }
+}