using System;

using System.Collections.Generic;

public interface ISubject<T>

{

    T Context { get; set; }

    void Attach(Action<T> observer);

    void Detach(Action<T> observer);

    void Notify();

}

​

public struct PieceOfData {

    public int Value { get; set; }

}

​

public class Subject : ISubject<PieceOfData>

{

    public PieceOfData Context { get; set; }

    private List<Action<PieceOfData>> _observers = new List<Action<PieceOfData>>();

    public void Attach(Action<PieceOfData> observer)

    {

        this._observers.Add(observer);

    }

​

    public void Detach(Action<PieceOfData> observer)

    {

        this._observers.Remove(observer);

    }

    public void Notify()

    {

        foreach (var observer in _observers)

        {

            observer.Invoke(this.Context);

        }

    }

}

​

public class Program

{

    public static void Main(string[] args)

    {

        var subject = new Subject

        {

            Context = new PieceOfData { Value = 10 }

        };

        subject.Attach((data) => Console.WriteLine(data.Value + 1));

        subject.Attach((data) => Console.WriteLine(data.Value * 2));

        subject.Attach((data) => Console.WriteLine((data.Value + 1) * 2));

        subject.Notify();

    }

}