From 744e5cd406d6e369c69add4933e3a06ac40cc0b5 Mon Sep 17 00:00:00 2001
From: Claudiu Farcas <claudiu.farcas@cgm.com>
Date: Sat, 17 Apr 2021 17:48:22 +0300
Subject: [PATCH] WIP more creational patterns

---
 Program.cs                              |   6 +-
 creational/prototype/PrototypeSample.cs |  19 +++++
 creational/singleton/SingletonSample.cs | 106 ++++++++++++++++++++++++
 3 files changed, 130 insertions(+), 1 deletion(-)
 create mode 100644 creational/prototype/PrototypeSample.cs
 create mode 100644 creational/singleton/SingletonSample.cs

diff --git a/Program.cs b/Program.cs
index 702a022..df6fd59 100644
--- a/Program.cs
+++ b/Program.cs
@@ -5,6 +5,8 @@ using design_patterns.creational.fluentbuilder;
 using design_patterns.creational.functionalbuilder;
 using design_patterns.creational.factory;
 using design_patterns.creational.facadebuilder;
+using design_patterns.creational.singleton;
+using design_patterns.creational.prototype;
 
 namespace design_patterns
 {
@@ -19,7 +21,9 @@ namespace design_patterns
                 // await AbstractFactorySample.Run();
                 // await FluentBuilderSample.Run();
                 // await FunctionalBuilderSample.Run();
-                await FacadeBuilderSample.Run();
+                // await FacadeBuilderSample.Run();
+                // await SingletonSample.Run();
+                await PrototypeSample.Run();
             }
             catch (System.Exception ex)
             {
diff --git a/creational/prototype/PrototypeSample.cs b/creational/prototype/PrototypeSample.cs
new file mode 100644
index 0000000..014676e
--- /dev/null
+++ b/creational/prototype/PrototypeSample.cs
@@ -0,0 +1,19 @@
+using System;
+using System.Threading.Tasks;
+
+namespace design_patterns.creational.prototype
+{
+    /// <summary>
+    /// Prototype is a creational design pattern that 
+    /// lets you copy (clone, deep copy) existing objects without making 
+    /// your code dependent on their classes.
+    /// </summary>
+    public class PrototypeSample
+    {
+        public static async Task Run()
+        {
+            Console.WriteLine("Creational - Prototype");
+
+        }
+    }
+}
\ No newline at end of file
diff --git a/creational/singleton/SingletonSample.cs b/creational/singleton/SingletonSample.cs
new file mode 100644
index 0000000..270f5ae
--- /dev/null
+++ b/creational/singleton/SingletonSample.cs
@@ -0,0 +1,106 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace design_patterns.creational.singleton
+{
+    /// <summary>
+    /// Singleton is a creational design pattern that 
+    /// lets you ensure that a class has only one instance, 
+    /// while providing a global access point to this instance.
+    /// 
+    /// https://refactoring.guru/design-patterns/singleton
+    /// </summary>
+    /// <remarks>
+    /// The Singleton pattern solves two problems at the same time, 
+    /// violating the Single Responsibility Principle:
+    /// 1. Ensure that a class has just a single instance. 
+    ///     (ex: shared resource, a database or a file)
+    /// 2. Provide a global access point to that instance. 
+    /// 
+    /// Solution:
+    /// - Make the default constructor private, to prevent other objects 
+    ///     from using the new operator with the Singleton class
+    /// - Create a static creation method that acts as a constructor. 
+    /// 
+    /// Problem:
+    /// - Testability
+    /// - usage of singleton leads to missuse and 
+    ///     wrong software design decisions
+    /// 
+    /// Solution:
+    /// - AVOID using singleton class, instead use DI containers 
+    ///     and configure the container to define lifetime of class as 
+    ///     as singleton
+    /// </remarks>
+    public class SingletonSample
+    {
+        public static async Task Run()
+        {
+            Console.WriteLine("Creational - Singleton");
+
+            var inst1 = SingletonDatabase.Instance;
+            var data = inst1.GetData(Guid.NewGuid().ToString());
+            Console.WriteLine($"data : {data}");
+
+            var inst2 = SingletonDatabase.Instance;
+            Console.WriteLine($"Are inst1 and inst2 the same? {inst1.Equals(inst2)}");
+
+            var task1 =  Task.Factory.StartNew(() => {
+                var instPerThread1 = PerThreadSingletonDatabase.Instance.GetData("pth");
+                Console.WriteLine($"instPerThread1 {instPerThread1}");
+            });
+            
+            var task2 = Task.Factory.StartNew(() => {
+                var instPerThread2 = PerThreadSingletonDatabase.Instance.GetData("pth");
+                Console.WriteLine($"instPerThread2 {instPerThread2}");
+            });
+            Task.WaitAll(task1, task2);
+
+        }
+    }
+
+    public interface IDatabase {
+        string GetData(string id);
+    }
+
+    /// <summary>
+    /// singleton class
+    /// </summary>
+    public class SingletonDatabase : IDatabase
+    {
+        private SingletonDatabase() {
+            //init resources
+            Console.WriteLine("singleton resources init");
+        }
+
+        // lazy initialization of the class
+        private static Lazy<SingletonDatabase> instance =  
+            new Lazy<SingletonDatabase>(() => new SingletonDatabase());
+        public static SingletonDatabase Instance { get { return instance.Value; } }
+        public string GetData(string id)
+        {
+            return $"Data {id}";
+        }
+    }
+
+    /// <summary>
+    /// singleton per thread
+    /// </summary>
+    public class PerThreadSingletonDatabase : IDatabase
+    {
+        private PerThreadSingletonDatabase() {
+            //init resources
+            Console.WriteLine("per thread singleton resources init");
+        }
+
+        // declare and instantiate object into local thread scope
+        private static ThreadLocal<PerThreadSingletonDatabase> threadInstance =  
+            new ThreadLocal<PerThreadSingletonDatabase>(() => new PerThreadSingletonDatabase());
+        public static PerThreadSingletonDatabase Instance { get { return threadInstance.Value; } }
+        public string GetData(string id)
+        {
+            return $"Data {id} from ThreadId: {Thread.CurrentThread.ManagedThreadId}";
+        }
+    }
+}
\ No newline at end of file