title: What are drawbacks or disadvantages of singleton pattern?
body: <p>The <a href="https://en.wikipedia.org/wiki/Singleton_pattern" rel="noreferrer">singleton pattern</a> is a fully paid up member of the <a href="https://en.wikipedia.org/wiki/Design_Patterns" rel="noreferrer">GoF</a>'s <a href="https://rads.stackoverflow.com/amzn/click/com/0201633612" rel="noreferrer" rel="nofollow noreferrer">patterns book</a>, but it lately seems rather orphaned by the developer world. I still use quite a lot of singletons, especially for <a href="https://en.wikipedia.org/wiki/Factory_method_pattern" rel="noreferrer">factory classes</a>, and while you have to be a bit careful about multithreading issues (like any class actually), I fail to see why they are so awful.</p>
  
  <p>Stack Overflow especially seems to assume that everyone agrees that Singletons are evil. Why?</p>
  
  <p>Please support your answers with "<em>facts, references, or specific expertise</em>"</p>