e.g. 5.18 Using a Delegate in an Extension Method

e.g. 5.19 Using the Filtering Extension Method with a Func

chap5_essential_language_features/essential_csharp_features/Program.cs

@@ -21,7 +21,14 @@ namespace automatically_implemented_properties
                 }
             };
             
-            foreach (Product prod in products.FilterByCategory("Soccer"))
+            Func<Product, bool> categoryFilter = delegate(Product prod)
+            {
+                return prod.Category == "Soccer";
+            };
+
+            IEnumerable<Product> filteredProducts = products.Filter(categoryFilter);
+            
+            foreach (Product prod in filteredProducts) 
             {
                 Console.WriteLine("Name: {0}, Price {1:c}", prod.Name, prod.Price);
             }
@@ -55,5 +62,17 @@ namespace automatically_implemented_properties
                 }
             }
         }
+
+        public static IEnumerable<Product> Filter(this IEnumerable<Product> productEnum,
+            Func<Product, bool> selectorParam)
+        {
+            foreach (Product prod in productEnum)
+            {
+                if (selectorParam(prod))
+                {
+                    yield return prod;
+                }
+            }
+        }
     }
 }