BAEL-2376 Inline classes in kotlin (#5842)

* BAEL-2376 Inline classes in kotlin

* BAEL-2376 Move classes

core-kotlin/src/main/kotlin/com/baeldung/inline/classes/CircleRadius.kt

@@ -0,0 +1,14 @@
+package com.baeldung.inline.classes
+
+interface Drawable {
+    fun draw()
+}
+
+inline class CircleRadius(private val circleRadius : Double) : Drawable {
+    val diameterOfCircle get() = 2 * circleRadius
+    fun areaOfCircle() = 3.14 * circleRadius * circleRadius
+
+    override fun draw() {
+        println("Draw my circle")
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/inline/classes/InlineDoubleWrapper.kt

@@ -0,0 +1,3 @@
+package com.baeldung.inline.classes
+
+inline class InlineDoubleWrapper(val doubleValue : Double)

core-kotlin/src/test/kotlin/com/baeldung/inline/classes/CircleRadiusTest.kt

@@ -0,0 +1,19 @@
+package com.baeldung.inline.classes
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class CircleRadiusTest {
+
+    @Test
+    fun givenRadius_ThenDiameterIsCorrectlyCalculated() {
+        val radius = CircleRadius(5.0)
+        assertEquals(10.0, radius.diameterOfCircle)
+    }
+
+    @Test
+    fun givenRadius_ThenAreaIsCorrectlyCalculated() {
+        val radius = CircleRadius(5.0)
+        assertEquals(78.5, radius.areaOfCircle())
+    }
+}

core-kotlin/src/test/kotlin/com/baeldung/inline/classes/InlineDoubleWrapperTest.kt

@@ -0,0 +1,13 @@
+package com.baeldung.inline.classes
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class InlineDoubleWrapperTest {
+
+    @Test
+    fun whenInclineClassIsUsed_ThenPropertyIsReadCorrectly() {
+        val piDoubleValue = InlineDoubleWrapper(3.14)
+        assertEquals(3.14, piDoubleValue.doubleValue)
+    }
+}