Singleton for Application Configuration

Question

In all my projects till now, I use to use singleton pattern to access Application configuration throughout the application. Lately I see lot of articles taking about not to use

Answer 1

If any component relies on configuration that can be changed at runtime (for example theme support for widgets), you need to provide some callback or signaling mechanism to notify about the changed config. That's why it is not enough to pass only the needed parameters to the component at creation time (like color). You also need to provide access to the config from inside of the component (pass complete config to component), or make a component factory that stores references to the config and all its created components so it can eventually apply the changes.

The former has the big downside that it clutters the constructors or blows up the interface, though it is maybe fastest for prototyping. If you take the "Law of Demeter" into account this is a big no because it violates encapsulation. The latter has the advantage that components keep their specific interface where components only take what they need, and as a bonus gives you a central place for refactoring (the factory). In the long run code maintenance will likely benefit from the factory pattern.

Also, even if the factory was a singleton, it would likely be used in far fewer places than a configuration singleton would have been.