Answer by CodeART for Alternatives to the singleton pattern

How about using IoC container? With some thought you can end up with something on the lines of:

Dependency.Resolve<IFoo>(); 

You would have to specify which implementation of IFoo to use at a startup, but this is a one off configuration which you can easily replace later. Lifetime of a resolved instance can be normally controlled by an IoC container.

Static singleton void method could be replaced with:

Dependency.Resolve<IFoo>().DoSomething();

Static singleton getter method could be replaced with:

var result = Dependency.Resolve<IFoo>().GetFoo();

Example is relevant to .NET, but I'm certain very similar can be achieved in other languages.