feat(#12): add abstractions in NotEmptyMutableCollection

src/main/kotlin/kotools/types/collections/NotEmptyMutableCollection.kt

@@ -8,5 +8,30 @@ import kotools.types.annotations.SinceKotoolsTypes
  * @param E The type of elements contained in this collection.
  */
 @SinceKotoolsTypes("1.3")
-internal sealed interface NotEmptyMutableCollection<E> : MutableCollection<E>,
-    NotEmptyCollection<E>
+public sealed interface NotEmptyMutableCollection<E> : MutableCollection<E>,
+    NotEmptyCollection<E> {
+    /**
+     * Inserts the [element] into this list at the specified [index], or throws
+     * an [IndexOutOfBoundsException] if the [index] is out of bounds.
+     */
+    @Throws(IndexOutOfBoundsException::class)
+    public fun add(index: Int, element: E)
+
+    /**
+     * Removes an element at the specified [index] from the list, or throws an
+     * [IndexOutOfBoundsException] if the index is out of bounds.
+     *
+     * Because this list shouldn't be empty, the element will not be removed if
+     * this list contains only one element.
+     */
+    @Throws(IndexOutOfBoundsException::class)
+    public infix fun removeAt(index: Int): E
+
+    /**
+     * Replaces the element at the specified [index] in this list with the
+     * specified [element], or throws an [IndexOutOfBoundsException] if the
+     * [index] is out of bounds.
+     */
+    @Throws(IndexOutOfBoundsException::class)
+    public fun set(index: Int, element: E): E
+}

src/main/kotlin/kotools/types/collections/NotEmptyMutableList.kt

@@ -96,11 +96,6 @@ public class NotEmptyMutableList<E>(override var head: E, vararg tail: E) :
 
     // ---------- Positional Access Operations ----------
 
-    /**
-     * Inserts the [element] into this list at the specified [index], or throws
-     * an [IndexOutOfBoundsException] if the [index] is out of bounds.
-     */
-    @Throws(IndexOutOfBoundsException::class)
     override fun add(index: Int, element: E): Unit = when (index) {
         in 1 until size -> tail.add(index - 1, element)
         0 -> {
@@ -113,26 +108,12 @@ public class NotEmptyMutableList<E>(override var head: E, vararg tail: E) :
 
     override fun get(index: Int): E = if (index == 0) head else tail[index - 1]
 
-    /**
-     * Removes an element at the specified [index] from the list, or throws an
-     * [IndexOutOfBoundsException] if the index is out of bounds.
-     *
-     * Because this list shouldn't be empty, the element will not be removed if
-     * this list contains only one element.
-     */
-    @Throws(IndexOutOfBoundsException::class)
-    override infix fun removeAt(index: Int): E = when (index) {
+    override fun removeAt(index: Int): E = when (index) {
         in 1 until size -> tail.removeAt(index - 1)
         0 -> head.also { if (tail.isNotEmpty()) head = tail.removeFirst() }
         else -> indexOutOfBounds(index, size)
     }
 
-    /**
-     * Replaces the element at the specified [index] in this list with the
-     * specified [element], or throws an [IndexOutOfBoundsException] if the
-     * [index] is out of bounds.
-     */
-    @Throws(IndexOutOfBoundsException::class)
     override fun set(index: Int, element: E): E = when (index) {
         in 1 until size -> element.also { tail[index - 1] = it }
         0 -> element.also { head = it }

src/test/kotlin/kotools/types/collections/NotEmptyMutableListTest.kt

@@ -92,7 +92,7 @@ class NotEmptyMutableListTest {
         }
 
         @Test
-        fun `should insert the element in the middle of the list with an index between 1 until the list's size`() {
+        fun `should insert the element into the list with an index in 1 until the list's size`() {
             // GIVEN
             val expectedList: NotEmptyList<String> =
                 NotEmptyList("one", "two", "three")