From be286cffbdb41d0dc70165b803b4b3a4c2ca67f8 Mon Sep 17 00:00:00 2001
From: Jason Zhu <jasonzhuyq@outlook.com>
Date: Mon, 12 Jul 2021 13:28:54 +1000
Subject: [PATCH] e.g. 5.18 Using a Delegate in an Extension Method e.g. 5.19
 Using the Filtering Extension Method with a Func

---
 .../essential_csharp_features/Program.cs      | 21 ++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/chap5_essential_language_features/essential_csharp_features/Program.cs b/chap5_essential_language_features/essential_csharp_features/Program.cs
index ee12b6b..78efcba 100644
--- a/chap5_essential_language_features/essential_csharp_features/Program.cs
+++ b/chap5_essential_language_features/essential_csharp_features/Program.cs
@@ -20,8 +20,15 @@ namespace automatically_implemented_properties
                     new Product {Name = "Corner flag", Category = "Soccer", Price = 34.95M}
                 }
             };
+            
+            Func<Product, bool> categoryFilter = delegate(Product prod)
+            {
+                return prod.Category == "Soccer";
+            };
 
-            foreach (Product prod in products.FilterByCategory("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;
+                }
+            }
+        }
     }
 }
\ No newline at end of file