feat!: v4.0 breaking API cleanup + explicitApi

BREAKING changes to the core:
- treeIterator is now a read-only `val`; added `iterator(order)` and use `asSequence(order)`.
- removeChild() only removes a direct child of the receiver; added `detach()` to unhook a node.
- addChild() rejects re-parenting and cycles (throws TreeNodeException); detach() first to move.
- clear() no longer nulls the receiver's own parent; only removes descendants.
- path() returns List<TreeNode<T>>? (null) instead of throwing.

Also:
- Enable strict explicitApi() across core + both modules; add explicit `public` modifiers.
- Update tests for the new contracts + add TreeNodeV4Test; refresh .api baselines.
- README + CHANGELOG (with migration notes); bump version to 4.0.0.

47 JVM tests green.

CHANGELOG.md

@@ -6,6 +6,33 @@ All notable changes to this project are documented here. The format is based on
 
 ## [Unreleased]
 
+## [4.0.0]
+
+A breaking release that cleans up the core API and enforces an explicit public surface.
+
+### Changed (breaking)
+- `TreeNode.treeIterator` is now a read-only `val` (set it via the constructor). Use
+  `iterator(order)` or `asSequence(order)` to traverse in a different order per call.
+- `removeChild(child)` now only removes a **direct** child of the receiver (previously it removed
+  the node from its actual parent regardless). Use `child.detach()` to unhook a node from wherever
+  it lives.
+- `addChild(child)` now throws `TreeNodeException` if `child` already has a parent or if the
+  attachment would create a cycle. Call `detach()` first to move a node.
+- `clear()` no longer detaches the receiver from its own parent; it only removes its descendants.
+- `path(descendant)` now returns `List<TreeNode<T>>?` (`null` when `descendant` is the root or not a
+  descendant) instead of throwing `TreeNodeException`.
+
+### Added
+- `TreeNode.detach()` — removes a node from its parent.
+- `TreeNode.iterator(order)` — a one-shot iterator in a specific order.
+- Strict `explicitApi()` mode across all modules.
+- New `tree-structure-compose` module: a `LazyTree` composable for Compose Multiplatform.
+
+### Migration
+- `node.treeIterator = PostOrder; for (n in node) { … }` → `for (n in node.asSequence(PostOrder)) { … }`
+- `root.removeChild(deepNode)` → `deepNode.detach()`
+- `try { node.path(x) } catch (e: TreeNodeException) { … }` → `node.path(x)?.let { … }`
+
 ## [3.4.0]
 
 ### Added
@@ -44,7 +71,8 @@ All notable changes to this project are documented here. The format is based on
 ## [3.1.3]
 - iOS targets and Maven Central (Sonatype Central Portal) publishing.
 
-[Unreleased]: https://github.com/AdrianKuta/Tree-Data-Structure/compare/v3.4.0...HEAD
+[Unreleased]: https://github.com/AdrianKuta/Tree-Data-Structure/compare/v4.0.0...HEAD
+[4.0.0]: https://github.com/AdrianKuta/Tree-Data-Structure/compare/v3.4.0...v4.0.0
 [3.4.0]: https://github.com/AdrianKuta/Tree-Data-Structure/compare/v3.1.5...v3.4.0
 [3.1.5]: https://github.com/AdrianKuta/Tree-Data-Structure/compare/v3.1.3...v3.1.5
 [3.1.4]: https://github.com/AdrianKuta/Tree-Data-Structure/releases/tag/v3.1.4

README.md

@@ -104,9 +104,8 @@ World
 val root = TreeNode("root")
 // ... build your tree
 
-// Choose iteration order (default is PreOrder)
+// Choose iteration order per call (the default order is set in the constructor and is read-only)
-root.treeIterator = TreeNodeIterators.PostOrder
+for (node in root.asSequence(TreeNodeIterators.PostOrder)) println(node.value)
-for (node in root) println(node.value)
 
 // Utilities
 root.nodeCount()   // number of descendants
@@ -114,10 +113,10 @@ root.height()      // longest path to a leaf (in edges)
 root.depth()       // distance from current node to the root
 val path = root.path(root.children.first()) // nodes from descendant up to root
 
-// Mutations
+// Mutations — removeChild removes a *direct* child; detach() unhooks a node from wherever it lives
 val child = root.children.first()
-root.removeChild(child)
+root.removeChild(child)   // child is now detached from root
-root.clear()       // remove entire subtree
+root.clear()              // remove all descendants of root
 ```
 
 ### Lazy traversal with Sequence

api/tree-structure.api

@@ -13,6 +13,7 @@ public class com/github/adriankuta/datastructure/tree/TreeNode : com/github/adri
 	public synthetic fun child (Ljava/lang/Object;Lkotlin/jvm/functions/Function1;)Lcom/github/adriankuta/datastructure/tree/TreeNode;
 	public final fun clear ()V
 	public final fun depth ()I
+	public final fun detach ()Z
 	public final fun getChildren ()Ljava/util/List;
 	public final fun getParent ()Lcom/github/adriankuta/datastructure/tree/TreeNode;
 	public final fun getTreeIterator ()Lcom/github/adriankuta/datastructure/tree/iterators/TreeNodeIterators;
@@ -20,11 +21,11 @@ public class com/github/adriankuta/datastructure/tree/TreeNode : com/github/adri
 	public final fun height ()I
 	public final fun isRoot ()Z
 	public fun iterator ()Ljava/util/Iterator;
+	public final fun iterator (Lcom/github/adriankuta/datastructure/tree/iterators/TreeNodeIterators;)Ljava/util/Iterator;
 	public final fun nodeCount ()I
 	public final fun path (Lcom/github/adriankuta/datastructure/tree/TreeNode;)Ljava/util/List;
 	public final fun prettyString ()Ljava/lang/String;
 	public final fun removeChild (Lcom/github/adriankuta/datastructure/tree/TreeNode;)Z
-	public final fun setTreeIterator (Lcom/github/adriankuta/datastructure/tree/iterators/TreeNodeIterators;)V
 	public fun toString ()Ljava/lang/String;
 }
 

build.gradle.kts

@@ -11,7 +11,7 @@ plugins {
 
 val PUBLISH_GROUP_ID = "com.github.adriankuta"
 val PUBLISH_ARTIFACT_ID = "tree-structure"    // base artifact; KMP will add -jvm, -ios*, etc.
-val PUBLISH_VERSION = "3.4.0"
+val PUBLISH_VERSION = "4.0.0"
 
 val snapshot: String? by project
 
@@ -60,6 +60,7 @@ repositories {
 }
 
 kotlin {
+    explicitApi()
     jvmToolchain(21)
 
     jvm()

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/ChildDeclarationInterface.kt

@@ -2,7 +2,7 @@ package com.github.adriankuta.datastructure.tree
 
 import kotlin.jvm.JvmSynthetic
 
-interface ChildDeclarationInterface<T> {
+public interface ChildDeclarationInterface<T> {
 
     /**
      * This method is used to easily create child in node.
@@ -20,5 +20,5 @@ interface ChildDeclarationInterface<T> {
      * @return New created TreeNode.
      */
     @JvmSynthetic
-    fun child(value: T, childDeclaration: ChildDeclaration<T>? = null): TreeNode<T>
+    public fun child(value: T, childDeclaration: ChildDeclaration<T>? = null): TreeNode<T>
 }

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/TreeNode.kt

@@ -27,14 +27,14 @@ import kotlin.jvm.JvmSynthetic
  * @param treeIterator the default traversal order used by [iterator]. Prefer the
  *   `asSequence(order)` / `preOrderSequence()` extensions to choose an order without mutating state.
  */
-open class TreeNode<T>(val value: T, var treeIterator: TreeNodeIterators = PreOrder) : Iterable<TreeNode<T>>, ChildDeclarationInterface<T> {
+public open class TreeNode<T>(public val value: T, public val treeIterator: TreeNodeIterators = PreOrder) : Iterable<TreeNode<T>>, ChildDeclarationInterface<T> {
 
     private var _parent: TreeNode<T>? = null
 
     /**
      * The converse notion of a child, an immediate ancestor.
      */
-    val parent: TreeNode<T>?
+    public val parent: TreeNode<T>?
         get() = _parent
 
     private val _children = mutableListOf<TreeNode<T>>()
@@ -42,28 +42,53 @@ open class TreeNode<T>(val value: T, var treeIterator: TreeNodeIterators = PreOr
     /**
      * A group of nodes with the same parent.
      */
-    val children: List<TreeNode<T>>
+    public val children: List<TreeNode<T>>
         get() = _children
 
     /**
      * Checks whether the current tree node is the root of the tree
      * @return `true` if the current tree node is root of the tree, `false` otherwise.
      */
-    val isRoot: Boolean
+    public val isRoot: Boolean
         get() = _parent == null
 
     /**
-     * Add new child to current node or root.
+     * Adds [child] as a direct child of this node.
      *
-     * @param child A node which will be directly connected to current node.
+     * @param child a node that is not already attached to a tree. To move a node that already has a
+     *   parent, call [detach] on it first.
+     * @throws TreeNodeException if [child] already has a parent, or if attaching it here would create
+     *   a cycle (i.e. [child] is this node or one of its ancestors).
      */
-    fun addChild(child: TreeNode<T>) {
+    public fun addChild(child: TreeNode<T>) {
+        if (child._parent != null) {
+            throw TreeNodeException("$child already has a parent; call detach() before re-attaching it.")
+        }
+        var ancestor: TreeNode<T>? = this
+        while (ancestor != null) {
+            if (ancestor === child) {
+                throw TreeNodeException("Adding $child here would create a cycle.")
+            }
+            ancestor = ancestor._parent
+        }
         child._parent = this
         _children.add(child)
     }
 
+    /**
+     * Detaches this node from its parent, removing it from the parent's [children].
+     *
+     * @return `true` if this node was attached and is now detached; `false` if it was already a root.
+     */
+    public fun detach(): Boolean {
+        val currentParent = _parent ?: return false
+        currentParent._children.remove(this)
+        _parent = null
+        return true
+    }
+
     @JvmSynthetic
-    override fun child(value: T, childDeclaration: ChildDeclaration<T>?): TreeNode<T> {
+    public override fun child(value: T, childDeclaration: ChildDeclaration<T>?): TreeNode<T> {
         val newChild = TreeNode(value)
         newChild._parent = this
         if (childDeclaration != null)
@@ -73,21 +98,24 @@ open class TreeNode<T>(val value: T, var treeIterator: TreeNodeIterators = PreOr
     }
 
     /**
-     * Removes a single instance of the specified node from this tree, if it is present.
+     * Removes [child] from this node's direct [children], if present.
      *
-     * @return `true` if the node has been successfully removed; `false` if it was not present in the tree.
+     * This only removes a *direct* child of the receiver; it does not reach into other nodes. To
+     * remove a node from wherever it currently lives, call [detach] on it instead.
+     *
+     * @return `true` if [child] was a direct child and has been removed; `false` otherwise.
      */
-    fun removeChild(child: TreeNode<T>): Boolean {
+    public fun removeChild(child: TreeNode<T>): Boolean {
-        val removed = child._parent?._children?.remove(child)
+        val removed = _children.remove(child)
-        child._parent = null
+        if (removed) child._parent = null
-        return removed ?: false
+        return removed
     }
 
     /**
      * This function go through tree and counts children. Root element is not counted.
      * @return All child and nested child count.
      */
-    fun nodeCount(): Int {
+    public fun nodeCount(): Int {
         var count = 0
         val stack = ArrayDeque<TreeNode<T>>()
         stack.addAll(_children)
@@ -102,7 +130,7 @@ open class TreeNode<T>(val value: T, var treeIterator: TreeNodeIterators = PreOr
     /**
      * @return The number of edges on the longest path between current node and a descendant leaf.
      */
-    fun height(): Int {
+    public fun height(): Int {
         var maxDepth = 0
         val stack = ArrayDeque<Pair<TreeNode<T>, Int>>()
         stack.addLast(this to 0)
@@ -118,7 +146,7 @@ open class TreeNode<T>(val value: T, var treeIterator: TreeNodeIterators = PreOr
      * Distance is the number of edges along the shortest path between two nodes.
      * @return The distance between current node and the root.
      */
-    fun depth(): Int {
+    public fun depth(): Int {
         var depth = 0
         var tempParent = parent
 
@@ -130,53 +158,52 @@ open class TreeNode<T>(val value: T, var treeIterator: TreeNodeIterators = PreOr
     }
 
     /**
-     * Returns the collection of nodes, which connect the current node
+     * Returns the chain of nodes from [descendant] up to and including this node, or `null` if
-     * with its descendants
+     * [descendant] is not a strict descendant of this node.
      *
-     * @param descendant the bottom child node for which the path is calculated
+     * @param descendant the node to walk up from.
-     * @return collection of nodes, which connect the current node with its descendants
+     * @return the path `[descendant, …, this]`, or `null` if [descendant] is the root or is not
-     * @throws TreeNodeException exception that may be thrown in case if the
+     *   located in this node's subtree.
-     *                           current node does not have such descendant or if the
-     *                           specified tree node is root
      */
-    @Throws(TreeNodeException::class)
+    public fun path(descendant: TreeNode<T>): List<TreeNode<T>>? {
-    fun path(descendant: TreeNode<T>): List<TreeNode<T>> {
+        if (descendant.isRoot) return null
-
         val path = mutableListOf<TreeNode<T>>()
         var node = descendant
         path.add(node)
         while (!node.isRoot) {
             node = node.parent!!
             path.add(node)
-            if (node == this)
+            if (node == this) return path
-                return path
         }
-        throw TreeNodeException("The specified tree node $descendant is not the descendant of tree node $this")
+        return null
     }
 
     /**
-     * Remove all children from root and every node in tree.
+     * Removes every descendant of this node. Afterwards [children] is empty and all former
+     * descendants are detached (their parent is `null`). This node itself stays attached to its own
+     * parent.
      */
-    fun clear() {
+    public fun clear() {
-        val all = ArrayDeque<TreeNode<T>>()
+        val descendants = ArrayDeque<TreeNode<T>>()
         val stack = ArrayDeque<TreeNode<T>>()
-        stack.addLast(this)
+        stack.addAll(_children)
         while (stack.isNotEmpty()) {
             val node = stack.removeLast()
-            all.addLast(node)
+            descendants.addLast(node)
             stack.addAll(node._children)
         }
-        all.forEach { node ->
+        descendants.forEach { node ->
             node._parent = null
             node._children.clear()
         }
+        _children.clear()
     }
 
-    override fun toString(): String {
+    public override fun toString(): String {
         return value.toString()
     }
 
-    fun prettyString(): String {
+    public fun prettyString(): String {
         val stringBuilder = StringBuilder()
         print(stringBuilder, "", "")
         return stringBuilder.toString()
@@ -198,9 +225,14 @@ open class TreeNode<T>(val value: T, var treeIterator: TreeNodeIterators = PreOr
     }
 
     /**
-     * You can change default iterator by changing [treeIterator] property.
+     * Returns an iterator over this node and its descendants using the default [treeIterator] order.
+     * Use [iterator] with an explicit order, or the `asSequence(order)` extension, to traverse in a
+     * different order without changing this node's default.
      */
-    override fun iterator(): Iterator<TreeNode<T>> = when (treeIterator) {
+    public override fun iterator(): Iterator<TreeNode<T>> = iterator(treeIterator)
+
+    /** Returns an iterator over this node and its descendants in the given [order]. */
+    public fun iterator(order: TreeNodeIterators): Iterator<TreeNode<T>> = when (order) {
         PreOrder -> PreOrderTreeIterator(this)
         PostOrder -> PostOrderTreeIterator(this)
         LevelOrder -> LevelOrderTreeIterator(this)

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/TreeNodeExt.kt

@@ -3,7 +3,7 @@ package com.github.adriankuta.datastructure.tree
 import com.github.adriankuta.datastructure.tree.iterators.TreeNodeIterators
 import kotlin.jvm.JvmSynthetic
 
-typealias ChildDeclaration<T> = ChildDeclarationInterface<T>.() -> Unit
+public typealias ChildDeclaration<T> = ChildDeclarationInterface<T>.() -> Unit
 
 /**
  * This method can be used to initialize new tree.
@@ -14,7 +14,7 @@ typealias ChildDeclaration<T> = ChildDeclarationInterface<T>.() -> Unit
  * @see [ChildDeclarationInterface.child]
  */
 @JvmSynthetic
-inline fun <reified T> tree(
+public inline fun <reified T> tree(
     root: T,
     defaultIterator: TreeNodeIterators = TreeNodeIterators.PreOrder,
     childDeclaration: ChildDeclaration<T>

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/TreeNodeFunctionalExt.kt

@@ -1,34 +1,34 @@
 package com.github.adriankuta.datastructure.tree
 
 /** Returns the first node (pre-order) whose value matches [predicate], or `null`. Short-circuits. */
-fun <T> TreeNode<T>.findNode(predicate: (T) -> Boolean): TreeNode<T>? =
+public fun <T> TreeNode<T>.findNode(predicate: (T) -> Boolean): TreeNode<T>? =
     preOrderSequence().firstOrNull { predicate(it.value) }
 
 /** All nodes (pre-order) whose value matches [predicate]. */
-fun <T> TreeNode<T>.filterNodes(predicate: (T) -> Boolean): List<TreeNode<T>> =
+public fun <T> TreeNode<T>.filterNodes(predicate: (T) -> Boolean): List<TreeNode<T>> =
     preOrderSequence().filter { predicate(it.value) }.toList()
 
 /** `true` if any node's value matches [predicate]. Short-circuits. */
-fun <T> TreeNode<T>.anyNode(predicate: (T) -> Boolean): Boolean =
+public fun <T> TreeNode<T>.anyNode(predicate: (T) -> Boolean): Boolean =
     preOrderSequence().any { predicate(it.value) }
 
 /** `true` if every node's value matches [predicate]. Short-circuits. */
-fun <T> TreeNode<T>.allNodes(predicate: (T) -> Boolean): Boolean =
+public fun <T> TreeNode<T>.allNodes(predicate: (T) -> Boolean): Boolean =
     preOrderSequence().all { predicate(it.value) }
 
 /** Counts nodes whose value matches [predicate]. */
-fun <T> TreeNode<T>.countNodes(predicate: (T) -> Boolean): Int =
+public fun <T> TreeNode<T>.countNodes(predicate: (T) -> Boolean): Int =
     preOrderSequence().count { predicate(it.value) }
 
 /** Folds [operation] over all nodes in pre-order, starting from [initial]. */
-fun <T, R> TreeNode<T>.foldNodes(initial: R, operation: (acc: R, node: TreeNode<T>) -> R): R =
+public fun <T, R> TreeNode<T>.foldNodes(initial: R, operation: (acc: R, node: TreeNode<T>) -> R): R =
     preOrderSequence().fold(initial) { acc, node -> operation(acc, node) }
 
 /**
  * Returns a new tree with the same shape whose values are produced by [transform]. The original is
  * left untouched. Stack-safe (iterative), so it handles arbitrarily deep trees.
  */
-fun <T, R> TreeNode<T>.mapValues(transform: (T) -> R): TreeNode<R> {
+public fun <T, R> TreeNode<T>.mapValues(transform: (T) -> R): TreeNode<R> {
     val newRoot = TreeNode(transform(value), treeIterator)
     val stack = ArrayDeque<Pair<TreeNode<T>, TreeNode<R>>>()
     stack.addLast(this to newRoot)
@@ -44,13 +44,13 @@ fun <T, R> TreeNode<T>.mapValues(transform: (T) -> R): TreeNode<R> {
 }
 
 /** Returns an independent deep copy of this subtree (same values, same shape, new nodes). */
-fun <T> TreeNode<T>.deepCopy(): TreeNode<T> = mapValues { it }
+public fun <T> TreeNode<T>.deepCopy(): TreeNode<T> = mapValues { it }
 
 /**
  * Structural equality: `true` when [other] holds the same values in the same shape. Unlike
  * [TreeNode]'s reference equality, this compares the entire subtree. Stack-safe.
  */
-fun <T> TreeNode<T>.structurallyEquals(other: TreeNode<T>): Boolean {
+public fun <T> TreeNode<T>.structurallyEquals(other: TreeNode<T>): Boolean {
     val stack = ArrayDeque<Pair<TreeNode<T>, TreeNode<T>>>()
     stack.addLast(this to other)
     while (stack.isNotEmpty()) {

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/TreeNodeNavigationExt.kt

@@ -1,13 +1,13 @@
 package com.github.adriankuta.datastructure.tree
 
 /** `true` when this node has no children. */
-val <T> TreeNode<T>.isLeaf: Boolean get() = children.isEmpty()
+public val <T> TreeNode<T>.isLeaf: Boolean get() = children.isEmpty()
 
 /** The number of direct children of this node. */
-val <T> TreeNode<T>.degree: Int get() = children.size
+public val <T> TreeNode<T>.degree: Int get() = children.size
 
 /** Walks up the parent chain and returns the topmost ancestor (the tree root). */
-fun <T> TreeNode<T>.root(): TreeNode<T> {
+public fun <T> TreeNode<T>.root(): TreeNode<T> {
     var node = this
     var parent = node.parent
     while (parent != null) {
@@ -18,7 +18,7 @@ fun <T> TreeNode<T>.root(): TreeNode<T> {
 }
 
 /** The chain of ancestors from the immediate [parent] up to (and including) the root. */
-fun <T> TreeNode<T>.ancestors(): List<TreeNode<T>> {
+public fun <T> TreeNode<T>.ancestors(): List<TreeNode<T>> {
     val result = mutableListOf<TreeNode<T>>()
     var parent = this.parent
     while (parent != null) {
@@ -29,13 +29,13 @@ fun <T> TreeNode<T>.ancestors(): List<TreeNode<T>> {
 }
 
 /** The other children of this node's parent (excludes this node). Empty for the root. */
-fun <T> TreeNode<T>.siblings(): List<TreeNode<T>> =
+public fun <T> TreeNode<T>.siblings(): List<TreeNode<T>> =
     parent?.children?.filter { it !== this } ?: emptyList()
 
 /** All leaf nodes in this subtree, in pre-order. */
-fun <T> TreeNode<T>.leaves(): List<TreeNode<T>> =
+public fun <T> TreeNode<T>.leaves(): List<TreeNode<T>> =
     preOrderSequence().filter { it.isLeaf }.toList()
 
 /** All nodes in this subtree except this node, in pre-order. */
-fun <T> TreeNode<T>.descendants(): List<TreeNode<T>> =
+public fun <T> TreeNode<T>.descendants(): List<TreeNode<T>> =
     preOrderSequence().filter { it !== this }.toList()

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/TreeNodeSequenceExt.kt

@@ -10,7 +10,7 @@ import com.github.adriankuta.datastructure.tree.iterators.TreeNodeIterators
  * traversal up front. Pairs with the Kotlin stdlib, e.g.
  * `root.asSequence().map { it.value }.firstOrNull { it == target }`.
  */
-fun <T> TreeNode<T>.asSequence(
+public fun <T> TreeNode<T>.asSequence(
     order: TreeNodeIterators = TreeNodeIterators.PreOrder,
 ): Sequence<TreeNode<T>> {
     val self = this
@@ -22,10 +22,10 @@ fun <T> TreeNode<T>.asSequence(
 }
 
 /** Lazy pre-order traversal as a [Sequence]. */
-fun <T> TreeNode<T>.preOrderSequence(): Sequence<TreeNode<T>> = asSequence(TreeNodeIterators.PreOrder)
+public fun <T> TreeNode<T>.preOrderSequence(): Sequence<TreeNode<T>> = asSequence(TreeNodeIterators.PreOrder)
 
 /** Lazy post-order traversal as a [Sequence]. */
-fun <T> TreeNode<T>.postOrderSequence(): Sequence<TreeNode<T>> = asSequence(TreeNodeIterators.PostOrder)
+public fun <T> TreeNode<T>.postOrderSequence(): Sequence<TreeNode<T>> = asSequence(TreeNodeIterators.PostOrder)
 
 /** Lazy level-order (breadth-first) traversal as a [Sequence]. */
-fun <T> TreeNode<T>.levelOrderSequence(): Sequence<TreeNode<T>> = asSequence(TreeNodeIterators.LevelOrder)
+public fun <T> TreeNode<T>.levelOrderSequence(): Sequence<TreeNode<T>> = asSequence(TreeNodeIterators.LevelOrder)

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/exceptions/TreeNodeException.kt

@@ -2,5 +2,5 @@ package com.github.adriankuta.datastructure.tree.exceptions
 
 import kotlin.jvm.JvmOverloads
 
-class TreeNodeException @JvmOverloads constructor(message: String? = null, cause: Throwable? = null) :
+public class TreeNodeException @JvmOverloads constructor(message: String? = null, cause: Throwable? = null) :
     RuntimeException(message, cause)

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/iterators/LevelOrderTreeIterator.kt

@@ -20,7 +20,7 @@ import com.github.adriankuta.datastructure.tree.TreeNode
  * Output: 1 2 3 4 5 6 7 8 9 10 11 12 13
  * ```
  */
-class LevelOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
+public class LevelOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
 
     private val stack = ArrayDeque<TreeNode<T>>()
 
@@ -28,9 +28,9 @@ class LevelOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
         stack.addLast(root)
     }
 
-    override fun hasNext(): Boolean = stack.isNotEmpty()
+    public override fun hasNext(): Boolean = stack.isNotEmpty()
 
-    override fun next(): TreeNode<T> {
+    public override fun next(): TreeNode<T> {
         val node =  stack.removeFirst()
         node.children
             .forEach { stack.addLast(it) }

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/iterators/PostOrderTreeIterator.kt

@@ -20,7 +20,7 @@ import com.github.adriankuta.datastructure.tree.TreeNode
  * Output: 10 5 11 12 13 6 2 3 7 8 9 4 1
  * ```
  */
-class PostOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
+public class PostOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
 
     private val result = ArrayDeque<TreeNode<T>>()
 
@@ -37,7 +37,7 @@ class PostOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
         }
     }
 
-    override fun hasNext(): Boolean = result.isNotEmpty()
+    public override fun hasNext(): Boolean = result.isNotEmpty()
 
-    override fun next(): TreeNode<T> = result.removeFirst()
+    public override fun next(): TreeNode<T> = result.removeFirst()
 }

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/iterators/PreOrderTreeIterator.kt

@@ -20,7 +20,7 @@ import com.github.adriankuta.datastructure.tree.TreeNode
  * Output: 1 2 5 10 6 11 12 13 3 4 7 8 9
  * ```
  */
-class PreOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
+public class PreOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
 
     private val stack = ArrayDeque<TreeNode<T>>()
 
@@ -28,9 +28,9 @@ class PreOrderTreeIterator<T>(root: TreeNode<T>) : Iterator<TreeNode<T>> {
         stack.addLast(root)
     }
 
-    override fun hasNext(): Boolean = stack.isNotEmpty()
+    public override fun hasNext(): Boolean = stack.isNotEmpty()
 
-    override fun next(): TreeNode<T> {
+    public override fun next(): TreeNode<T> {
         val node = stack.removeLast()
         node.children
             .asReversed()

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/iterators/TreeNodeIterators.kt

@@ -5,7 +5,7 @@ package com.github.adriankuta.datastructure.tree.iterators
  * @see PostOrder
  * @see LevelOrder
  */
-enum class TreeNodeIterators {
+public enum class TreeNodeIterators {
     /**
      * Tree is iterated by using `Pre-order Traversal Algorithm"
      * The pre-order traversal is a topologically sorted one,

src/commonTest/kotlin/com.github.adriankuta/datastructure.tree/TreeNodeStackSafetyTest.kt

@@ -37,13 +37,11 @@ class TreeNodeStackSafetyTest {
 
     @Test
     fun postOrderIterationDoesNotOverflowOnDeepTree() {
-        val tree = deepChain().apply { treeIterator = TreeNodeIterators.PostOrder }
+        assertEquals(depth + 1, deepChain().asSequence(TreeNodeIterators.PostOrder).count())
-        assertEquals(depth + 1, tree.toList().size)
     }
 
     @Test
     fun preOrderIterationDoesNotOverflowOnDeepTree() {
-        val tree = deepChain().apply { treeIterator = TreeNodeIterators.PreOrder }
+        assertEquals(depth + 1, deepChain().asSequence(TreeNodeIterators.PreOrder).count())
-        assertEquals(depth + 1, tree.toList().size)
     }
 }

src/commonTest/kotlin/com.github.adriankuta/datastructure.tree/TreeNodeTest.kt

@@ -51,7 +51,7 @@ class TreeNodeTest {
         )
 
         root.removeChild(curdNode)
-        root.removeChild(gingerTeaNode)
+        gingerTeaNode.detach()
         assertEquals(
             "Root\n" +
                     "└── Beverages\n" +

src/commonTest/kotlin/com.github.adriankuta/datastructure.tree/TreeNodeUtilitiesTest.kt

@@ -1,10 +1,9 @@
 package com.github.adriankuta.datastructure.tree
 
-import com.github.adriankuta.datastructure.tree.exceptions.TreeNodeException
 import kotlin.test.Test
 import kotlin.test.assertContentEquals
 import kotlin.test.assertEquals
-import kotlin.test.assertFailsWith
+import kotlin.test.assertNull
 
 class TreeNodeUtilitiesTest {
 
@@ -43,12 +42,12 @@ class TreeNodeUtilitiesTest {
     }
 
     @Test
-    fun pathThrowsWhenNotADescendant() {
+    fun pathReturnsNullWhenNotADescendant() {
-        assertFailsWith<TreeNodeException> { root.path(TreeNode(99)) }
+        assertNull(root.path(TreeNode(99)))
     }
 
     @Test
-    fun pathThrowsWhenDescendantIsRootItself() {
+    fun pathReturnsNullWhenDescendantIsRootItself() {
-        assertFailsWith<TreeNodeException> { root.path(root) }
+        assertNull(root.path(root))
     }
 }

src/commonTest/kotlin/com.github.adriankuta/datastructure.tree/TreeNodeV4Test.kt

@@ -0,0 +1,105 @@
+package com.github.adriankuta.datastructure.tree
+
+import com.github.adriankuta.datastructure.tree.exceptions.TreeNodeException
+import com.github.adriankuta.datastructure.tree.iterators.TreeNodeIterators
+import kotlin.test.Test
+import kotlin.test.assertContentEquals
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertFalse
+import kotlin.test.assertNull
+import kotlin.test.assertSame
+import kotlin.test.assertTrue
+
+class TreeNodeV4Test {
+
+    @Test
+    fun addChildRejectsNodeThatAlreadyHasAParent() {
+        val a = TreeNode("a")
+        val b = TreeNode("b")
+        a.addChild(b)
+
+        val other = TreeNode("other")
+        assertFailsWith<TreeNodeException> { other.addChild(b) }
+    }
+
+    @Test
+    fun addChildRejectsCycles() {
+        val root = TreeNode("root")
+        val child = TreeNode("child")
+        root.addChild(child)
+
+        // Attaching an ancestor under its own descendant would create a cycle.
+        assertFailsWith<TreeNodeException> { child.addChild(root) }
+        // Attaching a node under itself is also a cycle.
+        assertFailsWith<TreeNodeException> { root.addChild(root) }
+    }
+
+    @Test
+    fun detachRemovesFromParent() {
+        val root = TreeNode("root")
+        val child = TreeNode("child")
+        root.addChild(child)
+
+        assertTrue(child.detach())
+        assertNull(child.parent)
+        assertContentEquals(emptyList(), root.children)
+        // Detached node can now be re-attached elsewhere.
+        val newParent = TreeNode("newParent")
+        newParent.addChild(child)
+        assertSame(newParent, child.parent)
+    }
+
+    @Test
+    fun detachOnRootReturnsFalse() {
+        assertFalse(TreeNode("root").detach())
+    }
+
+    @Test
+    fun removeChildOnlyRemovesDirectChildren() {
+        val root = TreeNode("root")
+        val parent = TreeNode("parent")
+        val grandchild = TreeNode("grandchild")
+        root.addChild(parent)
+        parent.addChild(grandchild)
+
+        // grandchild is not a direct child of root -> no-op, returns false.
+        assertFalse(root.removeChild(grandchild))
+        assertSame(parent, grandchild.parent)
+
+        // direct child removal works.
+        assertTrue(parent.removeChild(grandchild))
+        assertNull(grandchild.parent)
+    }
+
+    @Test
+    fun clearOnNonRootKeepsItAttachedToItsParent() {
+        val root = TreeNode("root")
+        val branch = TreeNode("branch")
+        val leaf = TreeNode("leaf")
+        root.addChild(branch)
+        branch.addChild(leaf)
+
+        branch.clear()
+
+        assertContentEquals(emptyList(), branch.children)
+        assertSame(root, branch.parent)          // branch stays attached to root
+        assertContentEquals(listOf(branch), root.children)
+        assertNull(leaf.parent)                  // former descendant is detached
+    }
+
+    @Test
+    fun iteratorAcceptsExplicitOrderWithoutMutatingDefault() {
+        val tree = tree(1) {
+            child(2) { child(4) }
+            child(3)
+        }
+
+        val postOrder = tree.iterator(TreeNodeIterators.PostOrder).asSequence().map { it.value }.toList()
+        assertContentEquals(listOf(4, 2, 3, 1), postOrder)
+
+        // Default order is unchanged (PreOrder).
+        assertEquals(TreeNodeIterators.PreOrder, tree.treeIterator)
+        assertContentEquals(listOf(1, 2, 4, 3), tree.map { it.value })
+    }
+}

tree-structure-coroutines/build.gradle.kts

@@ -47,6 +47,7 @@ repositories {
 }
 
 kotlin {
+    explicitApi()
     jvmToolchain(21)
 
     jvm()

tree-structure-serialization/build.gradle.kts

@@ -48,6 +48,7 @@ repositories {
 }
 
 kotlin {
+    explicitApi()
     jvmToolchain(21)
 
     jvm()

tree-structure-serialization/src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/serialization/TreeNodeDto.kt

@@ -14,8 +14,8 @@ import kotlinx.serialization.Serializable
  */
 @Serializable
 public data class TreeNodeDto<T>(
-    val value: T,
+    public val value: T,
-    val children: List<TreeNodeDto<T>> = emptyList(),
+    public val children: List<TreeNodeDto<T>> = emptyList(),
 )
 
 /** Converts this subtree into a serializable [TreeNodeDto], preserving values and shape. */