Singleton Design Pattern in C#

Singleton Design Pattern?

A Singleton Ensures a class has only one instance and provides a global point of access to it.
A single constructor, that is private and parameterless.
The class type is sealed.
A static variable that holds a reference to the single created instance, if any.
A public static means of getting the reference to the single created instance, creating one if necessary.

The important advantages of a Singleton Pattern are listed below:

• Singleton can be lazy loaded.
• Singleton helps to hide dependencies.
• Singleton pattern can be implemented interfaces.
• Singleton can be also inherit from other classes.
• Singleton has Static Initialization.
• Singleton provides a single point of access to a particular instance, so it is easy to maintain.
• Singleton can be extended into a factory pattern.

Singleton Design Pattern Disadvantages 

• Hard to switch for a mock object(Unit testing)
• This pattern reduces the potential for parallelism within a program