Updated delegate addition and removal examples (#945)

Author: pkulikov

csharp/language-reference/operators/SubtractionOperator.cs

@@ -7,6 +7,8 @@ public static class SubtractionOperator
         public static void Examples()
         {
             DelegateRemoval();
+            DelegateRemovalNoChange();
+            DelegateRemovalAndNull();
             SubtractAndAssign();
         }
 
@@ -25,14 +27,49 @@ private static void DelegateRemoval()
             abba();  // output: abba
             Console.WriteLine();
 
+            var nihil = abbaab - abbaab;
+            Console.WriteLine(nihil is null);  // output: True
+            // </SnippetDelegateRemoval>
+        }
+
+        private static void DelegateRemovalNoChange()
+        {
+            // <SnippetDelegateRemovalNoChange>
+            Action a = () => Console.Write("a");
+            Action b = () => Console.Write("b");
+
+            var abbaab = a + b + b + a + a + b;
             var aba = a + b + a;
+            
             var first = abbaab - aba;
             first();  // output: abbaab
             Console.WriteLine();
+            Console.WriteLine(object.ReferenceEquals(abbaab, first));  // output: True
 
-            var nihil = abbaab - abbaab;
-            Console.WriteLine(nihil is null);  // output: True
-            // </SnippetDelegateRemoval>
+            Action a2 = () => Console.Write("a");
+            var changed = aba - a;
+            changed();  // output: ab
+            Console.WriteLine();
+            var unchanged = aba - a2;
+            unchanged();  // output: aba
+            Console.WriteLine();
+            Console.WriteLine(object.ReferenceEquals(aba, unchanged));  // output: True
+            // </SnippetDelegateRemovalNoChange>
+        }
+
+        private static void DelegateRemovalAndNull()
+        {
+            // <SnippetDelegateRemovalAndNull>
+            Action a = () => Console.Write("a");
+
+            var nothing = null - a;
+            Console.WriteLine(nothing is null);  // output: True
+
+            var first = a - null;
+            a();  // output: a
+            Console.WriteLine();
+            Console.WriteLine(object.ReferenceEquals(first, a));  // output: True
+            // </SnippetDelegateRemovalAndNull>
         }
 
         private static void SubtractAndAssign()

snippets/csharp/language-reference/operators/AdditionExamples.cs

@@ -41,36 +41,35 @@ private static void StringConcatenation()
         private static void AddDelegates()
         {
             // <SnippetAddDelegates>
-            Action<int> printDouble = (int s) => Console.WriteLine(2 * s);
-            Action<int> printTriple = (int s) => Console.WriteLine(3 * s);
-            Action<int> combined = printDouble + printTriple;
-            combined(5);
-            // Output:
-            // 10
-            // 15
+            Action a = () => Console.Write("a");
+            Action b = () => Console.Write("b");
+            Action ab = a + b;
+            ab();  // output: ab
             // </SnippetAddDelegates>
+            Console.WriteLine();
         }
 
         private static void AddAndAssign()
         {
             // <SnippetAddAndAssign>
-            int a = 5;
-            a += 9;
-            Console.WriteLine(a);
+            int i = 5;
+            i += 9;
+            Console.WriteLine(i);
             // Output: 14
 
             string story = "Start. ";
             story += "End.";
             Console.WriteLine(story);
             // Output: Start. End.
 
-            Action<int> printer = (int s) => Console.WriteLine(s);
-            printer += (int s) => Console.WriteLine(2 * s);
-            printer(3);
-            // Output:
-            // 3
-            // 6
+            Action printer = () => Console.Write("a");
+            printer();  // output: a
+            
+            Console.WriteLine();
+            printer += () => Console.Write("b");
+            printer();  // output: ab
             // </SnippetAddAndAssign>
+            Console.WriteLine();
         }
     }
 }