Initial data commit

Task/Singleton/C-sharp/singleton-1.cs

@@ -0,0 +1,16 @@
+public sealed class Singleton1 //Lazy: Yes ||| Thread-safe: Yes ||| Uses locking: Yes
+{
+    private static Singleton1 instance;
+    private static readonly object lockObj = new object();
+
+    public static Singleton1 Instance {
+        get {
+            lock(lockObj) {
+                if (instance == null) {
+                    instance = new Singleton1();
+                }
+            }
+            return instance;
+        }
+    }
+}

Task/Singleton/C-sharp/singleton-2.cs

@@ -0,0 +1,18 @@
+public sealed class Singleton2 //Lazy: Yes ||| Thread-safe: Yes ||| Uses locking: Yes, but only once
+{
+    private static Singleton2 instance;
+    private static readonly object lockObj = new object();
+
+    public static Singleton2 Instance {
+        get {
+            if (instance == null) {
+                lock(lockObj) {
+                    if (instance == null) {
+                        instance = new Singleton2();
+                    }
+                }
+            }
+            return instance;
+        }
+    }
+}

Task/Singleton/C-sharp/singleton-3.cs

@@ -0,0 +1,6 @@
+public sealed class Singleton3 //Lazy: Yes, but not completely ||| Thread-safe: Yes ||| Uses locking: No
+{
+    private static Singleton3 Instance { get; } = new Singleton3();
+
+    static Singleton3() { }
+}

Task/Singleton/C-sharp/singleton-4.cs

@@ -0,0 +1,11 @@
+public sealed class Singleton4 //Lazy: Yes ||| Thread-safe: Yes ||| Uses locking: No
+{
+    public static Singleton4 Instance => SingletonHolder.instance;
+
+    private class SingletonHolder
+    {
+        static SingletonHolder() { }
+
+        internal static readonly Singleton4 instance = new Singleton4();
+    }
+}

Task/Singleton/C-sharp/singleton-5.cs

@@ -0,0 +1,6 @@
+public sealed class Singleton5 //Lazy: Yes ||| Thread-safe: Yes ||| Uses locking: No
+{
+    private static readonly Lazy<Singleton5> lazy = new Lazy<Singleton5>(() => new Singleton5());
+
+    public static Singleton5 Instance => lazy.Value;
+}