Add back interface equality but limit to only matching types

osu.Game/Beatmaps/BeatmapInfo.cs

@@ -163,6 +163,8 @@ namespace osu.Game.Beatmaps
             return false;
         }
 
+        public bool Equals(IBeatmapInfo other) => other is BeatmapInfo b && Equals(b);
+
         public bool AudioEquals(BeatmapInfo other) => other != null && BeatmapSet != null && other.BeatmapSet != null &&
                                                       BeatmapSet.Hash == other.BeatmapSet.Hash &&
                                                       (Metadata ?? BeatmapSet.Metadata).AudioFile == (other.Metadata ?? other.BeatmapSet.Metadata).AudioFile;

osu.Game/Beatmaps/BeatmapSetInfo.cs

@@ -78,6 +78,8 @@ namespace osu.Game.Beatmaps
             return false;
         }
 
+        public bool Equals(IBeatmapSetInfo other) => other is BeatmapSetInfo b && Equals(b);
+
         #region Implementation of IHasOnlineID
 
         int IHasOnlineID<int>.OnlineID => OnlineID ?? -1;

osu.Game/Beatmaps/IBeatmapInfo.cs

@@ -1,6 +1,7 @@
 // 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.Database;
 using osu.Game.Rulesets;
 
@@ -11,7 +12,7 @@ namespace osu.Game.Beatmaps
     /// <summary>
     /// A single beatmap difficulty.
     /// </summary>
-    public interface IBeatmapInfo : IHasOnlineID<int>
+    public interface IBeatmapInfo : IHasOnlineID<int>, IEquatable<IBeatmapInfo>
     {
         /// <summary>
         /// The user-specified name given to this beatmap.

osu.Game/Beatmaps/IBeatmapSetInfo.cs

@@ -12,7 +12,7 @@ namespace osu.Game.Beatmaps
     /// <summary>
     /// A representation of a collection of beatmap difficulties, generally packaged as an ".osz" archive.
     /// </summary>
-    public interface IBeatmapSetInfo : IHasOnlineID<int>
+    public interface IBeatmapSetInfo : IHasOnlineID<int>, IEquatable<IBeatmapSetInfo>
     {
         /// <summary>
         /// The date when this beatmap was imported.

osu.Game/Models/RealmBeatmap.cs

@@ -106,6 +106,8 @@ namespace osu.Game.Models
             return ID == other.ID;
         }
 
+        public bool Equals(IBeatmapInfo? other) => other is RealmBeatmap b && Equals(b);
+
         public bool AudioEquals(RealmBeatmap? other) => other != null
                                                         && BeatmapSet != null
                                                         && other.BeatmapSet != null

osu.Game/Models/RealmBeatmapSet.cs

@@ -64,6 +64,8 @@ namespace osu.Game.Models
 
         public override string ToString() => Metadata?.GetDisplayString() ?? base.ToString();
 
+        public bool Equals(IBeatmapSetInfo? other) => other is RealmBeatmapSet b && Equals(b);
+
         IEnumerable<IBeatmapInfo> IBeatmapSetInfo.Beatmaps => Beatmaps;
 
         IEnumerable<INamedFileUsage> IBeatmapSetInfo.Files => Files;

osu.Game/Online/API/Requests/Responses/APIBeatmap.cs

@@ -103,5 +103,7 @@ namespace osu.Game.Online.API.Requests.Responses
         public string Hash => throw new NotImplementedException();
 
         #endregion
+
+        public bool Equals(IBeatmapInfo? other) => other is APIBeatmap b && Equals(b);
     }
 }

osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs

@@ -141,5 +141,7 @@ namespace osu.Game.Online.API.Requests.Responses
         double IBeatmapSetInfo.MaxBPM => BPM;
 
         #endregion
+
+        public bool Equals(IBeatmapSetInfo? other) => other is APIBeatmapSet b && Equals(b);
     }
 }