====== Singleton ======
===== Singleton vs. static class =====
**Singleton**
  * + we can use singletons as parameters
  * + control over instantion 

**Static class**
  * - lazy initialization
  * + easier


===== Implementations =====

==== With locks ====
  * Standard solution using locks.

<code csharp>
public sealed class Singleton
{
    static Singleton _instance=null;
    static readonly object _lock = new object();

    Singleton()
    {
    }

    public static Singleton Instance
    {
        get
        {
            lock (_lock)
            {
                if (_instance==null)
                {
                    _instance = new Singleton();
                }
                return _instance;
            }
        }
    }
}

</code>


==== Without locks ====
  * Elegant solution without locks.

<code csharp>
public sealed class Singleton
{
    static readonly Singleton _instance=new Singleton();

    static Singleton()
    {
    }

    Singleton()
    {
    }

    public static Singleton Instance
    {
        get
        {
            return _instance;
        }
    }
}

</code>

==== Without cycle ====
  * Solves complications if one static constructor invokes another which invokes the first again. Solution breaks the cycle.

<code csharp>
public sealed class Singleton
{
    Singleton()
    {
    }

    public static Singleton Instance
    {
        get
        {
            return Nested.instance;
        }
    }
    
    class Nested
    {
        static Nested()
        {
        }

        internal static readonly Singleton instance = new Singleton();
    }
}


</code>

===== Refrences =====

  * [[http://www.yoda.arachsys.com/csharp/singleton.html]]
  * [[http://dotnet.dzone.com/news/c-singleton-pattern-vs-static-]]