Angular relies on singletons for all its services, however using singletons is often frowned upon in the development community.
Despite this controversy, I personally find Angular to be a valuable and effective tool. What am I overlooking?
Angular relies on singletons for all its services, however using singletons is often frowned upon in the development community.
Despite this controversy, I personally find Angular to be a valuable and effective tool. What am I overlooking?
The concept of the Singleton pattern is incredibly valuable. It is difficult to fathom creating software without it! Just picture constantly recreating an object that hashes a million records.
However, the challenges arise in its implementation:
What makes singletons problematic?
Typically used as a global instance, why is this frowned upon? By making something global, you are concealing the dependencies of your application within your code instead of exposing them through interfaces. Relying on something being global to avoid passing it around signifies poor coding practices.
Singletons violate the principle of single responsibility: they manage their own creation and lifecycle.
They inherently lead to tightly coupled code which can complicate testing scenarios in many cases.
They retain state throughout the application's lifespan, posing challenges for testing as tests may need to be ordered, going against the fundamental principle of independent unit tests.
Most critiques seem to target an outdated approach to implementing the singleton pattern, where instances are globally accessible:
public class ClassicSingleton {
private static ClassicSingleton instance = null;
protected ClassicSingleton() {
// Existent solely to prevent instantiation.
}
public static ClassicSingleton getInstance() {
if(instance == null) {
instance = new ClassicSingleton();
}
return instance;
}
}
Utilizing a dependency injection container (such as Angular or Spring) helps alleviate most of these concerns. The container manages the lifecycle and injects the singleton instance into client code. This allows for easy substitution of the injected singleton for testing purposes.
Essentially, leveraging a DI container facilitates the usage of singletons without encountering potential drawbacks.
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