Singleton Vs ServiceLocator

Question

What are the advantages and disadvantages of using a Service Locator versus a singleton? I've read that singletons are bad but I'm wondering if s Service Locator would be generally a better way of doing things.

Answer 1

Both approaches are bad in that it's not obvious from class contract what are its' dependencies. That is,

private void foo()
{
    var x = SomeSingleton.Instance.GetX();
    var y = ServiceLocator.GetService<IProvider>().GetY();
}

has references to SomeSingleton and IProvider buried deep somewhere inside.

However, compared to pure singleton approach, service locators are generally much better in that they allow for simpler centralized configuration, lifetime management, etc. They also allow for better testability (you can always mock calls to GetService<T>), lower coupling, separation of concerns, etc.

Answer 2

if testability is a concern, using service locator is much better then pure singletons.