What is a singleton pattern?

Purpose:

• Design pattern knowledge is a good indicator of programmer competency.
• The lowest bar and easiest example is the Singleton
• This is basically an idiot test to see if a developer has any pattern knowledge.
• Not being able to answer this question would be a serious concern.

Potential Answer:
The singleton pattern is a software design pattern that restricts the instantiation of a class to one object.

If you want to stand out perhaps raise how the singleton is overused and can be considered an anti-pattern when used incorrectly:

• Introduces unnecessary restrictions when a sole instance not really required
• Singleton makes code more complex, less useful and harder to tests
• Debugging can be hard to figure out which code path lead to singleton's current state
• Memory allocated cannot be freed
• Excessive use will promote procedural programming over object orientated