Add factory to GetState (#515)

* Add factory to GetState

* Update src/Neo.VM/ExecutionContext.cs

* ut

* Improve ut

src/Neo.VM/ExecutionContext.cs

@@ -146,12 +146,13 @@ public ExecutionContext Clone(int initialPosition)
         /// Gets custom data of the specified type. If the data does not exist, create a new one.
         /// </summary>
         /// <typeparam name="T">The type of data to be obtained.</typeparam>
+        /// <param name="factory">A delegate used to create the entry. If factory is null, new() will be used.</param>
         /// <returns>The custom data of the specified type.</returns>
-        public T GetState<T>() where T : class, new()
+        public T GetState<T>(Func<T>? factory = null) where T : class, new()
         {
             if (!shared_states.States.TryGetValue(typeof(T), out object? value))
             {
-                value = new T();
+                value = factory is null ? new T() : factory();
                 shared_states.States[typeof(T)] = value;
             }
             return (T)value;

tests/Neo.VM.Tests/UtExecutionContext.cs

@@ -8,11 +8,28 @@ namespace Neo.Test
     [TestClass]
     public class UtExecutionContext
     {
+        class TestState
+        {
+            public bool Flag = false;
+        }
+
         [TestMethod]
         public void StateTest()
         {
             var context = new ExecutionContext(Array.Empty<byte>(), -1, new ReferenceCounter());
 
+            // Test factory
+
+            var flag = context.GetState(() => new TestState() { Flag = true });
+            Assert.IsTrue(flag.Flag);
+
+            flag.Flag = false;
+
+            flag = context.GetState(() => new TestState() { Flag = true });
+            Assert.IsFalse(flag.Flag);
+
+            // Test new
+
             var stack = context.GetState<Stack<int>>();
             Assert.AreEqual(0, stack.Count);
             stack.Push(100);