I should point out that the same issue exists with class instances. They can be inappropriately passed to constructors violating certain design guidelines. Bad object oriented design is always possible! (There are more wrong things to do than right ones!).

However, the point about being global is off the mark, because in that case, it’s the point! If you only want one instance of a class, then clearly any client that needs an instance of that class has to use that one existing Singleton instance. Whether that one instance is used inappropriately is a different matter.

While global variables are generally bad because of the scoping issue, if an attribute could be added to a global variable to prevent other instances of the variable’s type, it would be like a Singleton, but it would only be bad if the global type wasn’t scoped, such as class methods (and classes in namespaces). (Of course, Class names are global too unless they’re in a namespace, and there is nothing to prevent putting any class, including a Singleton class, in a namespace).

In this case, by design, a single instance of a class is desired, and a Singleton is the only way to do this. (That’s by definition – any pattern that does this is a type of Singleton pattern).

Now, a good question is which Singleton pattern is best. Scott Meyer’s, and others, have addresses this issue.

never let truth get in the way of a good story.

IOC, solves this problem by removing global state. So I don’t think we are talking about the same thing.