diff --git a/src/DataStructure/CacheItem.cs b/src/DataStructure/CacheItem.cs
index dc06044..7c4ac24 100644
--- a/src/DataStructure/CacheItem.cs
+++ b/src/DataStructure/CacheItem.cs
@@ -1,5 +1,3 @@
-using System.Diagnostics;
-
 namespace Skeleton.DataStructure;
 
 /// <summary>
@@ -8,16 +6,12 @@ namespace Skeleton.DataStructure;
 public class CacheItem
 {
 
-    public CacheItem(Func<CacheItem, object> cal) => ProxyCalculator = cal;
-    
-    public static readonly CacheItem Null = new CacheItem<bool>(x => false);
     /// <summary>
     ///     if the item needs update
     /// </summary>
     public bool Expired { get; protected set; } = true;
-    internal HashSet<CacheItem> References { get; set; } = new();
-    internal HashSet<CacheItem> Dependencies { get; set; } = new();
-    private Func<object> Calculator => () => ProxyCalculator(this);
+    public HashSet<CacheItem> References { get; set; } = new();
+    public HashSet<CacheItem> Dependencies { get; set; } = new();
     /// <summary>
     ///     tag the item and all dependencies as out dated
     /// </summary>
@@ -29,76 +23,48 @@ public class CacheItem
                 c.Expire();
     }
     
-    public TObject Get<TObject>() => (this as CacheItem<TObject>)!.Get;
-    private object? Value { get; set; }
-    public void Assign(object o) => UpdateCalculation(x => o);
-    public object Get()
-    {
-        if (Expired)
-        {
-            Value = Calculator();
-            Expired = false;
-        }
-        return Value!;
-    }
-
-    public TObject GetFrom<TObject>(CacheItem item) => (this as CacheItem<TObject>)!.GetFrom(item);
-
-    public object GetFrom(CacheItem item)
-    {
-        References.Add(item);
-        item.Dependencies.Add(this);
-        return Get();
-    }
-
-    public Func<CacheItem, object> ProxyCalculator { get; internal set; }
-
-    public void UpdateCalculation(Func<CacheItem, object> a) => ProxyCalculator = a;
 }
 
 /// <inheritdoc />
 public class CacheItem<TObject> : CacheItem
 {
+    public static readonly CacheItem<TObject> Null = new();
     /// <summary>
     ///     construct by provide a method to update the value
     /// </summary>
     /// <param name="rec"></param>
-    public CacheItem(Func<CacheItem, TObject> rec) : base(x => rec(x))
-    {
-    }
+    public CacheItem(Func<CacheItem?, TObject> rec) => ProxyCalculator = rec;
 
-    private TObject? Value { get; set; }
+    public CacheItem() => ProxyCalculator = c => default;
+
+    protected TObject? Value { get; set; }
     /// <summary>
     ///     return cached/updated value when reference is not used to calculate another cache item
     /// </summary>
-    public new TObject Get
+    public virtual TObject? Get
     {
         get
         {
             if (Expired)
             {
-                Value = Calculator();
+                Value = ProxyCalculator(this);
                 Expired = false;
             }
-            return Value!;
+            return Value;
         }
     }
-    private Func<TObject> Calculator => () => ProxyCalculator(this);
 
     /// <summary>
     /// provide trace information while calculating
     /// </summary>
-    public new Func<CacheItem, TObject> ProxyCalculator
-    {
-        get => x => (TObject)base.ProxyCalculator(x); 
-        set => base.ProxyCalculator = x => value(x)!;
-    }
+    public Func<CacheItem, TObject?> ProxyCalculator { get; set; }
+
     /// <summary>
     ///     trace the dependency and return cached value/updated value
     /// </summary>
     /// <param name="d"></param>
     /// <returns></returns>
-    public new TObject GetFrom(CacheItem d)
+    public TObject? GetFrom(CacheItem d)
     {
         References.Add(d);
         d.Dependencies.Add(this);
@@ -108,7 +74,7 @@ public class CacheItem<TObject> : CacheItem
     /// update the formula of item value
     /// </summary>
     /// <param name="val"></param>
-    public void UpdateCalculation(Func<CacheItem, TObject> val)
+    public void UpdateCalculation(Func<CacheItem, TObject?> val)
     {
         Expire();
         foreach (CacheItem item in Dependencies)
@@ -117,7 +83,6 @@ public class CacheItem<TObject> : CacheItem
         ProxyCalculator = val;
     }
     
-
     public void Assign(TObject b) => UpdateCalculation(x => b);
 
 }