refactor: 💡 extract traversal actions to outer

core/src/main/kotlin/tw/xcc/gumtree/helper/TraversalHelper.kt

@@ -4,38 +4,36 @@ import tw.xcc.gumtree.api.tree.Tree
 
 private fun <T : Tree> preOrderedImpl(
     tree: T,
-    visited: MutableList<T>
+    action: (T) -> Unit
 ) {
-    visited.add(tree)
+    action(tree)
     tree.getChildren().forEach {
         @Suppress("UNCHECKED_CAST")
-        preOrderedImpl(it as T, visited)
+        preOrderedImpl(it as T, action)
     }
 }
 
 private fun <T : Tree> postOrderedImpl(
     tree: T,
-    visited: MutableList<T>
+    action: (T) -> Unit
 ) {
     tree.getChildren().forEach {
         @Suppress("UNCHECKED_CAST")
-        postOrderedImpl(it as T, visited)
+        postOrderedImpl(it as T, action)
     }
-    visited.add(tree)
+    action(tree)
 }
 
-fun <T : Tree> preOrdered(tree: T): List<T> {
-    synchronized(tree) {
-        val visited = mutableListOf<T>()
-        preOrderedImpl(tree, visited)
-        return visited.toList()
-    }
+fun <T : Tree> preOrdered(
+    tree: T,
+    action: (T) -> Unit
+) = synchronized(tree) {
+    preOrderedImpl(tree, action)
 }
 
-fun <T : Tree> postOrdered(tree: T): List<T> {
-    synchronized(tree) {
-        val visited = mutableListOf<T>()
-        postOrderedImpl(tree, visited)
-        return visited.toList()
-    }
+fun <T : Tree> postOrdered(
+    tree: T,
+    action: (T) -> Unit
+) = synchronized(tree) {
+    postOrderedImpl(tree, action)
 }

core/src/main/kotlin/tw/xcc/gumtree/model/BasicTree.kt

@@ -47,16 +47,24 @@ abstract class BasicTree<T> : Tree, Traversable<T> where T : BasicTree<T> {
         }
     }
 
+    final override fun preOrdered(): List<T> {
+        val result = mutableListOf<T>()
+        preOrdered(self) { result.add(it) }
+        return result
+    }
+
+    final override fun postOrdered(): List<T> {
+        val result = mutableListOf<T>()
+        postOrdered(self) { result.add(it) }
+        return result
+    }
+
     final override fun getParent(): T? = synchronized(this) { parent.get() }
 
     final override fun getChildren(): List<T> = synchronized(this) { childrenMap.get().values.toList() }
 
     final override fun childAt(i: Int): T? = synchronized(this) { childrenMap.get()[i] }
 
-    final override fun preOrdered(): List<T> = preOrdered(self)
-
-    final override fun postOrdered(): List<T> = postOrdered(self)
-
     final override fun childCount(): Int = synchronized(this) { childrenMap.get().size }
 
     final override fun isRoot(): Boolean = synchronized(this) { parent.get() == null }