Add getErrorOrElse

Matches getOrElse signature with respect to the error.

src/main/kotlin/com/github/michaelbull/result/Get.kt

@@ -66,3 +66,14 @@ infix inline fun <V, E> Result<V, E>.getOrElse(transform: (E) -> V): V {
         is Err -> transform(error)
     }
 }
+
+/**
+ * @param transform The transformation to apply to the [value][Ok.value].
+ * @return The [error][Err.error] if [Err], otherwise the [transformed][transform] [value][Ok.value].
+ */
+infix inline fun <V, E> Result<V, E>.getErrorOrElse(transform: (V) -> E): E {
+    return when (this) {
+        is Ok -> transform(value)
+        is Err -> error
+    }
+}

src/test/kotlin/com/github/michaelbull/result/GetTest.kt

@@ -64,4 +64,16 @@ internal class GetTest {
         val value = Err("hello").getOrElse { "world" }
         assertThat(value, equalTo("world"))
     }
+
+    @Test
+    internal fun `getErrorOrElse should return the transformed result value if ok`() {
+        val error = Ok("hello").getErrorOrElse { "world" }
+        assertThat(error, equalTo("world"))
+    }
+
+    @Test
+    internal fun `getErrorOrElse should return the result error if not ok`() {
+        val error = Err("hello").getErrorOrElse { "world" }
+        assertThat(error, equalTo("hello"))
+    }
 }