A-M baby

Task/History-variables/C-sharp/history-variables.cs

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+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace History
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            var h = new HistoryObject();
+            h.Value = 5;
+            h.Value = "foo";
+            h.Value += "bar";
+
+            var history = h.ToArray();
+
+            for (int i = 0; i < history.Length; i++)
+            {
+                Console.Write("{0}{1}", history[i], ((i >= history.Length - 1) ? "\n" : " <- "));
+            }
+
+            h.Undo();
+            h.Undo();
+            h.Undo();
+
+            Console.WriteLine(h.Value);
+        }
+
+        private class HistoryObject : IEnumerable<object>
+        {
+            public HistoryObject()
+            {
+                _history = new Stack<object>(); // Initiates the history stack.
+            }
+
+            public object Value
+            {
+                get // Returns the top value from the history if there is one. Otherwise null.
+                {
+                    if (_history.Count > 0)
+                        return _history.Peek();
+                    return null;
+                }
+                set { _history.Push(value); } // Adds the specified value to the history.
+            }
+
+            public void Undo()
+            {
+                if (_history.Count > 0)
+                    _history.Pop(); // Removes the current value from the history.
+            }
+
+            // History stack that will hold all previous values of the object.
+            private readonly Stack<object> _history;
+
+            public IEnumerator<object> GetEnumerator()
+            {
+                return _history.GetEnumerator();
+            }
+
+            IEnumerator IEnumerable.GetEnumerator()
+            {
+                return GetEnumerator();
+            }
+        }
+    }
+}