add kcp

Src/Core/Optional/Optional.cs

@@ -7,11 +7,11 @@
     }
     public interface IOptional<T>
     {
-        bool Allow { get; }
-        T Value { get; }
+        bool Allow { get; set; }
+        T Value { get; set; }
     }
     [System.Serializable]
-    public record Optional<T> : IOptional<T>
+    public class Optional<T> : IOptional<T>
     {
 #if NET5_0_OR_GREATER
         bool allow;
@@ -23,8 +23,18 @@
         T value;
 #endif
         public bool Allow { get => allow; set => allow = value;}
-        public T Value { get => value; set => this.value = value; }
-        public void SetValueThenAllow(T newValue) => value = newValue;
+        public T Value
+        {
+            get => value;
+            set=>this.value=value;
+        }
+
+        public void SetValueThenAllow(T newValue)
+        {
+            value = newValue;
+            allow = true;
+        }
+
         public void Clear()
         {
             Allow = false;