ExDM- Harmonize the code with the 01-DelegateEventsScript.md document #…

…404

- Updated sample code for delegates.
- UT 👍

ExDataManagement/FunctionalProgramming/FunctionalProgramming.UnitTest/AnonymousFunctionsUnitTest.cs

@@ -19,6 +19,17 @@ namespace TP.FunctionalProgramming
   [TestClass]
   public class AnonymousFunctionsUnitTest
   {
+    /// <summary>
+    /// While raising this delegate variable the null-conditional operator is not applied.
+    /// Hence, this argument must not be null to prevent throwing an exception.
+    /// </summary>
+    [TestMethod]
+    public void NullCallBack()
+    {
+      AnonymousFunctions _newInstance = new AnonymousFunctions();
+      Assert.ThrowsException<NullReferenceException>(() => _newInstance.ConsistencyCheck(null));
+    }
+
     [TestMethod]
     public void NamedMethodCallBackTest()
     {

ExDataManagement/FunctionalProgramming/FunctionalProgramming.UnitTest/DelegateExampleUnitTest.cs

@@ -1,6 +1,6 @@
 //____________________________________________________________________________________________________________________________________
 //
-//  Copyright (C) 2023, Mariusz Postol LODZ POLAND.
+//  Copyright (C) 2024, Mariusz Postol LODZ POLAND.
 //
 //  To be in touch join the community by pressing the `Watch` button and get started commenting using the discussion panel at
 //
@@ -14,9 +14,48 @@
 
 namespace TP.FunctionalProgramming
 {
+  /// <summary>
+  /// This testing class reveals features of delegate.
+  /// </summary>
   [TestClass]
   public class DelegateExampleUnitTest
   {
+    /// <summary>
+    /// Typically the delegate value is instantiated using a new operator.
+    /// It is possible to instantiate the delegate value by applying more concise syntax
+    /// using only the method name or definition of the anonymous function.
+    /// </summary>
+    [TestMethod]
+    public void Instantiation()
+    {
+      DelegateExample _newInstance = new DelegateExample();
+      _newInstance.PerformCalculationVar = new DelegateExample.PerformCalculation(PerformSumMethod);// Delegate value instantiation using new operator
+      Assert.IsNotNull(_newInstance.PerformCalculationVar);
+      Assert.AreEqual<int>(5, _newInstance.PerformCalculationVar(2, 2));
+      _newInstance = new DelegateExample();
+      _newInstance.PerformCalculationVar = PerformSumMethod; // Auto instantiation using only method name.
+                                                             // It looks like assignment of a method to delegate variable
+      Assert.IsNotNull(_newInstance.PerformCalculationVar);
+      Assert.AreEqual<int>(5, _newInstance.PerformCalculationVar(2, 2));
+      _newInstance.PerformCalculationVar = (x, y) => x + y + 1;
+      Assert.IsNotNull(_newInstance.PerformCalculationVar);
+      Assert.AreEqual<int>(5, _newInstance.PerformCalculationVar(2, 2));
+    }
+
+    /// <summary>
+    /// The delegate variable is of reference type - the null value can be assigned.
+    /// It indicates that invocation of the delegate variable containing null throws an exception.
+    /// Thanks to the null-conditional operator nothing is invoked if the delegate variable evaluates to null
+    /// </summary>
+    [TestMethod]
+    public void NullInvocation()
+    {
+      DelegateExample _newInstance = new DelegateExample();
+      _newInstance.PerformCalculationVar = null;
+      Assert.ThrowsException<NullReferenceException>(() => _newInstance.PerformCalculationVar(0, 0));
+      _newInstance.PerformCalculationVar?.Invoke(0, 0); //thanks to the null-conditional operator nothing is invoked
+    }
+
     [TestMethod]
     public void SumTestMethod()
     {
@@ -63,6 +102,12 @@ public void PerformSumMethodCalledTest()
       Assert.AreSame(_args, EventArgs.Empty);
     }
 
+    /// <summary>
+    /// This function adds the values of two integers and returns the result incremented by 1.
+    /// </summary>
+    /// <param name="x">The first parameter used by the add operation</param>
+    /// <param name="y">The second parameter used by the add operation</param>
+    /// <returns>the sum of x and y parameters incremented by 1</returns>
     private int PerformSumMethod(int x, int y)
     {
       checked

ExDataManagement/FunctionalProgramming/FunctionalProgramming/AnonymousFunctions.cs

@@ -34,6 +34,18 @@ public class AnonymousFunctions
 
     internal delegate void CallBackTestDelegate(bool testResult);
 
+    /// <summary>
+    /// Invoking this method the consistency of this state machine is checked. 
+    /// The result is transferred to the user through the <paramref name="testResult"/> delegate pointing 
+    /// out a method invoked to transfer the check result. While raising this delegate variable 
+    /// the null-conditional operator is not applied. Hence, this argument must not be null to prevent 
+    /// throwing an exception.
+    /// </summary>
+    /// <param name="testResult">This parameter contains a delegate value pointing out a method invoked 
+    /// to transfer the check result. This argument must not be null to prevent throwing an exception.
+    /// </param>
+    /// <exception cref="NullReferenceException">exception thrown if the <paramref name="testResult"/> evaluates to null.
+    /// </exception>
     [Conditional("DEBUG")]
     internal void ConsistencyCheck(CallBackTestDelegate testResult)
     {

ExDataManagement/FunctionalProgramming/FunctionalProgramming/DelegateExample.cs

@@ -26,7 +26,7 @@ public class DelegateExample
     /// The perform calculation variable
     /// </summary>
     /// <returns>System.Int32.</returns>
-    public PerformCalculation PerformCalculationVar;
+    public PerformCalculation PerformCalculationVar = null;
 
     /// <summary>
     /// An example of event
@@ -38,8 +38,6 @@ public class DelegateExample
     /// </summary>
     public DelegateExample()
     {
-      PerformCalculationVar = new PerformCalculation(PerformSumMethod);
-      PerformCalculationVar = new PerformCalculation(PerformSubtractMethod);
       //PerformCalculationVar = new PerformCalculation(PerformSubtractDoubleMethod); //No overload for 'DelegateExample.PerformSubtractDoubleMethod(double, double)' matches delegate 'DelegateExample.PerformCalculation'
     }