DesignPatterns

Practical implementations of classic design patterns in C# / .NET 9. Each pattern is a small, self-contained console project built around a realistic use case rather than abstract Foo/Bar examples.

Patterns

Pattern	Category	Use case	Project
Singleton	Creational	Thread-safe in-memory cache shared across the whole application	src/SingletonPattern
Factory Method	Creational	Notification dispatcher for SMS, Email, WhatsApp and Telegram	src/FactoryPattern

More patterns are being added over time.

Singleton — In-Memory Cache

InMemoryCache exposes a single shared instance through Lazy<T>, so the instance is created on first use and creation is thread-safe without explicit locks. The storage itself is a ConcurrentDictionary, so concurrent reads and writes are safe too. The class is sealed with a private constructor, so no other instance can be created.

InMemoryCache.Instance.Set("User_1", "Test User Data");
var user = InMemoryCache.Instance.Get("User_1");

Factory Method — Notification Dispatcher

MessageFactory creates the right IMessageService implementation for a given MessageType. Client code depends only on the IMessageService abstraction, never on concrete providers, which keeps it decoupled and easy to test.

var sms = MessageFactory.CreateService(MessageType.Sms);
sms.Send("+1234567890", "Your verification code is 5542.");

Running

Requires the .NET 9 SDK.

git clone https://github.com/Martik2002/DesignPatterns.git
cd DesignPatterns

dotnet run --project src/SingletonPattern
dotnet run --project src/FactoryPattern

License

MIT