Singleton

- Ensure a class has one instance, and 
- provide a global point of access to it.

Benefits

1. It doesn’t create the instance if no one uses it
2. It’s initialized at runtime.
3. You can subclass the singleton

Avoid Singleton unless unavoidable

Poorly designed singletons are often “helpers” that add functionality to another class. If you can, just move all of that behavior into the Manager class it helps.

• Can make code less readable
• They encourage coupling.
• Difficult to be concurrency-friendly
• Lazy initialization takes control away from you

Alternatives

• Pass instance
• Store insatnce in a base class
• Use preexisting global class
• Service Locator

Single thread implementation

public class SimpleSingleton
{
    private static SimpleSingleton instance;
    
    //private constructor to not allow external initialization
    private SimpleSingleton() { }

    //static method to intialize class without creating class instance
    public static SimpleSingleton Instance
    {
        get
        {
            if (instance == null)
            {
                instance = new SimpleSingleton();
            }
            return instance;
        }
    }
}