adding packages

deprecated/undo/lib/src/simple_stack.dart

@@ -0,0 +1,43 @@
+import 'package:undo/undo.dart';
+
+class SimpleStack<T> extends ChangeStack {
+  /// Simple stack for keeping track of changes and easy callback for new state changes
+  SimpleStack(
+    this._state, {
+    int? limit,
+    this.onUpdate,
+  }) : super(limit: limit) {
+    if (onUpdate != null) {
+      onUpdate!(_state);
+    }
+  }
+
+  late T _state;
+
+  /// Current state
+  T get state => _state;
+
+  set state(T val) => modify(val);
+
+  void Function(T val)? onUpdate;
+
+  void modify(T val) {
+    try {
+      add(Change<T>(
+        _state,
+        () => _newValue(val),
+        _newValue,
+      ));
+    } catch (e) {
+      rethrow;
+    }
+  }
+
+  void _newValue(T val) {
+    _state = val;
+
+    if (onUpdate != null) {
+      onUpdate!(val);
+    }
+  }
+}