Make MultiplayerRoomUser equatable

osu.Game/Online/RealtimeMultiplayer/MultiplayerRoomUser.cs

@@ -1,21 +1,41 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System;
 using osu.Game.Users;
 
 namespace osu.Game.Online.RealtimeMultiplayer
 {
-    public class MultiplayerRoomUser
+    public class MultiplayerRoomUser : IEquatable<MultiplayerRoomUser>
     {
         public MultiplayerRoomUser(in int userId)
         {
             UserID = userId;
         }
 
-        public long UserID { get; set; }
+        public long UserID { get; }
 
         public MultiplayerUserState State { get; set; }
 
         public User User { get; set; }
+
+        public bool Equals(MultiplayerRoomUser other)
+        {
+            if (ReferenceEquals(null, other)) return false;
+            if (ReferenceEquals(this, other)) return true;
+
+            return UserID == other.UserID;
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (ReferenceEquals(null, obj)) return false;
+            if (ReferenceEquals(this, obj)) return true;
+            if (obj.GetType() != this.GetType()) return false;
+
+            return Equals((MultiplayerRoomUser)obj);
+        }
+
+        public override int GetHashCode() => UserID.GetHashCode();
     }
 }