Answer.

Dependency lifecycle management is the organization of creating, initializing, updating, and destroying application components in such a way that they are independent of each other and easily testable. IoC containers (Inversion of Control) and the Dependency Injection (DI) pattern are often used for this purpose.

IoC container allows:

• Automatically creating and linking objects (components).
• Managing the lifetime (scope) of each object (singleton, transient, scoped).
• Providing easy replaceability of components for testing and scaling.

Example in C# using Microsoft.Extensions.DependencyInjection:

public interface IMessageSender { void Send(string msg); }
public class EmailSender : IMessageSender {
    public void Send(string msg) { /* send email */ }
}

// Registering dependencies
var services = new ServiceCollection();
services.AddScoped<IMessageSender, EmailSender>();

// Getting an instance
var provider = services.BuildServiceProvider();
var sender = provider.GetService<IMessageSender>();
sender.Send("Hello!");

Key features:

• Allows clearly separating dependencies and accelerating architecture development.
• Simplifies testing of components by replacing dependencies (mocks).
• Helps achieve loose coupling of components.

Trick questions.

What is the difference between Dependency Injection (DI) and the Service Locator pattern, and why is Service Locator considered an anti-pattern?

Service Locator violates the explicit passing of dependencies, making the code less transparent. It is better to use DI through constructor or methods so that the compiler can check the correctness of dependencies.

// Bad: Service Locator
var sender = ServiceLocator.Get<IMessageSender>();

// Good: via DI
public class MyService {
   public MyService(IMessageSender sender) { ... }
}

What is the difference between the Singleton pattern and Single Instance lifetime in a DI container?

The Singleton pattern is implemented manually and does not depend on the container; Single Instance provides an instance from the container, which is safer for unit tests and extensions.

Should dependencies be injected in all classes, even simple utilities?

No. Utilities without dependencies or weakly coupled helper classes (for example, a class for mathematical constants) do not need to have DI injected — this complicates the code without providing benefits.