using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        HashSet<Tweet> tweets = new HashSet<Tweet>();

        var tweet = new Tweet();

        tweet.id = 1;

        tweet.text = "hi";

        tweets.Add(tweet);

        tweets.Add(tweet);

        Console.WriteLine(tweets.Count);

    }

}

​

public class Tweet

{

    public int id { get; set ; }

    public string text { get; set; }

}