C# Design Pattern Examples

LazySimpleSingleton.cs

public class SimpleSingleton{
  private int count = 1;

  // Use lazy<T> to delay initialisation until the field is accessed
  private static readonly Lazy<SimpleSingleton> _instance = new Lazy<SimpleSingleton>( ()=> new SimpleSingleton());

  private SimpleSingleton(){
    Console.WriteLine($"{nameof(SimpleSingleton)} constructor called at {DateTime.Now}");
  }

  public static SimpleSingleton Instance{
    get => _instance.Value;
  }

  public int Count{get  => count;}

  public void IncrementCount(){
    count++;
  }
}

SimpleSingleton.cs

/// <summary>
/// A simple 'thread-safe' Singleton implementation with no 'Lazy Loading'
/// </summary>
public class SimpleSingleton{
  private int count = 1;

  private static readonly SimpleSingleton _instance = new SimpleSingleton();

  private SimpleSingleton(){
    Console.WriteLine($"{nameof(SimpleSingleton)} constructor called at {DateTime.Now}");
  }

  public static SimpleSingleton Instance{
    get => _instance;
  }

  public int Count{get  => count;}

  public void IncrementCount(){
    count++;
  }
}


// TEST CODE
public class Program
{
  public static void Main()
  {
    var obj1 = SimpleSingleton.Instance;
    var obj2 = SimpleSingleton.Instance;

    // Test that obj1 and obj2 are indeed point to the same instance of our SimpleSingleton
    Console.WriteLine(obj1.Count);
    obj1.IncrementCount();

    // Count should now be incremented in 'both' objects
    Console.WriteLine(obj1.Count);
    Console.WriteLine(obj2.Count); 

  }
}