From a67e156883fb6f80aa10e3af6701ae2417181c48 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 12 Nov 2021 18:09:45 +0900
Subject: [PATCH 01/14] Add `IBeatmapInfo` equality support

---
 osu.Game/Beatmaps/BeatmapInfo.cs                  | 11 +++++++++++
 osu.Game/Beatmaps/IBeatmapInfo.cs                 |  3 ++-
 osu.Game/Models/RealmBeatmap.cs                   | 15 +++++++++++++++
 .../Online/API/Requests/Responses/APIBeatmap.cs   | 12 ++++++++++++
 4 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/osu.Game/Beatmaps/BeatmapInfo.cs b/osu.Game/Beatmaps/BeatmapInfo.cs
index 5bbd48f26d..ea2346f060 100644
--- a/osu.Game/Beatmaps/BeatmapInfo.cs
+++ b/osu.Game/Beatmaps/BeatmapInfo.cs
@@ -151,6 +151,17 @@ namespace osu.Game.Beatmaps
 
         public override string ToString() => this.GetDisplayTitle();
 
+        public bool Equals(IBeatmapInfo other)
+        {
+            if (other is BeatmapInfo b)
+                return Equals(b);
+
+            if (OnlineID > 0 && other?.OnlineID > 0)
+                return other.OnlineID == OnlineID;
+
+            return false;
+        }
+
         public bool Equals(BeatmapInfo other)
         {
             if (ID == 0 || other?.ID == 0)
diff --git a/osu.Game/Beatmaps/IBeatmapInfo.cs b/osu.Game/Beatmaps/IBeatmapInfo.cs
index 84ea6d3019..ab096b8897 100644
--- a/osu.Game/Beatmaps/IBeatmapInfo.cs
+++ b/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.
diff --git a/osu.Game/Models/RealmBeatmap.cs b/osu.Game/Models/RealmBeatmap.cs
index 9311425cb7..d1907d3ffd 100644
--- a/osu.Game/Models/RealmBeatmap.cs
+++ b/osu.Game/Models/RealmBeatmap.cs
@@ -98,6 +98,21 @@ namespace osu.Game.Models
 
         #endregion
 
+        #region Implementation of IEquatable<IBeatmapInfo>
+
+        public bool Equals(IBeatmapInfo? other)
+        {
+            if (other is RealmBeatmap b)
+                return b.ID == ID;
+
+            if (OnlineID > 0 && other?.OnlineID > 0)
+                return other.OnlineID == OnlineID;
+
+            return false;
+        }
+
+        #endregion
+
         public bool AudioEquals(RealmBeatmap? other) => other != null
                                                         && BeatmapSet != null
                                                         && other.BeatmapSet != null
diff --git a/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs b/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
index 2560502173..33098a2919 100644
--- a/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
+++ b/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
@@ -103,5 +103,17 @@ namespace osu.Game.Online.API.Requests.Responses
         public string Hash => throw new NotImplementedException();
 
         #endregion
+
+        #region Implementation of IEquatable<IBeatmapInfo>
+
+        public bool Equals(IBeatmapInfo? other)
+        {
+            if (OnlineID > 0 && other?.OnlineID > 0)
+                return other.OnlineID == OnlineID;
+
+            return false;
+        }
+
+        #endregion
     }
 }

From 54cd1158a4b198e55d6747fd98124e50d29aa401 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 12 Nov 2021 18:14:11 +0900
Subject: [PATCH 02/14] Add `IBeatmapSetInfo` equality support

---
 osu.Game/Beatmaps/BeatmapSetInfo.cs                 | 11 +++++++++++
 osu.Game/Beatmaps/IBeatmapSetInfo.cs                |  2 +-
 osu.Game/Models/RealmBeatmapSet.cs                  | 13 ++++++++++++-
 .../Online/API/Requests/Responses/APIBeatmapSet.cs  | 12 ++++++++++++
 4 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/osu.Game/Beatmaps/BeatmapSetInfo.cs b/osu.Game/Beatmaps/BeatmapSetInfo.cs
index 0c93c4b9db..5bdaf26471 100644
--- a/osu.Game/Beatmaps/BeatmapSetInfo.cs
+++ b/osu.Game/Beatmaps/BeatmapSetInfo.cs
@@ -66,6 +66,17 @@ namespace osu.Game.Beatmaps
 
         public bool Protected { get; set; }
 
+        public bool Equals(IBeatmapSetInfo other)
+        {
+            if (other is BeatmapSetInfo b)
+                return Equals(b);
+
+            if (OnlineID > 0 && other?.OnlineID > 0)
+                return other.OnlineID == OnlineID;
+
+            return false;
+        }
+
         public bool Equals(BeatmapSetInfo other)
         {
             if (other == null)
diff --git a/osu.Game/Beatmaps/IBeatmapSetInfo.cs b/osu.Game/Beatmaps/IBeatmapSetInfo.cs
index 20c46d9063..67f38397d4 100644
--- a/osu.Game/Beatmaps/IBeatmapSetInfo.cs
+++ b/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.
diff --git a/osu.Game/Models/RealmBeatmapSet.cs b/osu.Game/Models/RealmBeatmapSet.cs
index 6735510422..ddf2cf48fa 100644
--- a/osu.Game/Models/RealmBeatmapSet.cs
+++ b/osu.Game/Models/RealmBeatmapSet.cs
@@ -53,7 +53,16 @@ namespace osu.Game.Models
         /// <param name="filename">The name of the file to get the storage path of.</param>
         public string? GetPathForFile(string filename) => Files.SingleOrDefault(f => string.Equals(f.Filename, filename, StringComparison.OrdinalIgnoreCase))?.File.StoragePath;
 
-        public override string ToString() => Metadata?.ToString() ?? base.ToString();
+        public bool Equals(IBeatmapSetInfo? other)
+        {
+            if (other is RealmBeatmap b)
+                return b.ID == ID;
+
+            if (OnlineID > 0 && other?.OnlineID > 0)
+                return other.OnlineID == OnlineID;
+
+            return false;
+        }
 
         public bool Equals(RealmBeatmapSet? other)
         {
@@ -72,6 +81,8 @@ namespace osu.Game.Models
             return ReferenceEquals(this, other);
         }
 
+        public override string ToString() => Metadata?.ToString() ?? base.ToString();
+
         IEnumerable<IBeatmapInfo> IBeatmapSetInfo.Beatmaps => Beatmaps;
 
         IEnumerable<INamedFileUsage> IBeatmapSetInfo.Files => Files;
diff --git a/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs b/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
index 168e9d5d51..f4515c4258 100644
--- a/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
+++ b/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
@@ -141,5 +141,17 @@ namespace osu.Game.Online.API.Requests.Responses
         double IBeatmapSetInfo.MaxBPM => BPM;
 
         #endregion
+
+        #region Implementation of IEquatable<IBeatmapSetInfo>
+
+        public bool Equals(IBeatmapSetInfo? other)
+        {
+            if (OnlineID > 0 && other?.OnlineID > 0)
+                return other.OnlineID == OnlineID;
+
+            return false;
+        }
+
+        #endregion
     }
 }

From 7349e5521a0dbbb73b50ad7bbbab2f8e7db19c26 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 12 Nov 2021 18:10:06 +0900
Subject: [PATCH 03/14] Update `BeatmapCollection` to use `IBeatmapInfo`

---
 osu.Game/Collections/BeatmapCollection.cs        | 2 +-
 osu.Game/Collections/CollectionFilterDropdown.cs | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/osu.Game/Collections/BeatmapCollection.cs b/osu.Game/Collections/BeatmapCollection.cs
index 7e4b15ecf9..1a739f824f 100644
--- a/osu.Game/Collections/BeatmapCollection.cs
+++ b/osu.Game/Collections/BeatmapCollection.cs
@@ -25,7 +25,7 @@ namespace osu.Game.Collections
         /// <summary>
         /// The beatmaps contained by the collection.
         /// </summary>
-        public readonly BindableList<BeatmapInfo> Beatmaps = new BindableList<BeatmapInfo>();
+        public readonly BindableList<IBeatmapInfo> Beatmaps = new BindableList<IBeatmapInfo>();
 
         /// <summary>
         /// The date when this collection was last modified.
diff --git a/osu.Game/Collections/CollectionFilterDropdown.cs b/osu.Game/Collections/CollectionFilterDropdown.cs
index 7067f82fd3..ad23874b2e 100644
--- a/osu.Game/Collections/CollectionFilterDropdown.cs
+++ b/osu.Game/Collections/CollectionFilterDropdown.cs
@@ -39,7 +39,7 @@ namespace osu.Game.Collections
         }
 
         private readonly IBindableList<BeatmapCollection> collections = new BindableList<BeatmapCollection>();
-        private readonly IBindableList<BeatmapInfo> beatmaps = new BindableList<BeatmapInfo>();
+        private readonly IBindableList<IBeatmapInfo> beatmaps = new BindableList<IBeatmapInfo>();
         private readonly BindableList<CollectionFilterMenuItem> filters = new BindableList<CollectionFilterMenuItem>();
 
         [Resolved(CanBeNull = true)]
@@ -200,7 +200,7 @@ namespace osu.Game.Collections
             private IBindable<WorkingBeatmap> beatmap { get; set; }
 
             [CanBeNull]
-            private readonly BindableList<BeatmapInfo> collectionBeatmaps;
+            private readonly BindableList<IBeatmapInfo> collectionBeatmaps;
 
             [NotNull]
             private readonly Bindable<string> collectionName;

From 1c49c4a6029942c8fa8a07efe18a2a34534597a1 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 12 Nov 2021 18:32:39 +0900
Subject: [PATCH 04/14] Fix incorrect type check

---
 osu.Game/Models/RealmBeatmapSet.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/osu.Game/Models/RealmBeatmapSet.cs b/osu.Game/Models/RealmBeatmapSet.cs
index ddf2cf48fa..3217abb419 100644
--- a/osu.Game/Models/RealmBeatmapSet.cs
+++ b/osu.Game/Models/RealmBeatmapSet.cs
@@ -55,7 +55,7 @@ namespace osu.Game.Models
 
         public bool Equals(IBeatmapSetInfo? other)
         {
-            if (other is RealmBeatmap b)
+            if (other is RealmBeatmapSet b)
                 return b.ID == ID;
 
             if (OnlineID > 0 && other?.OnlineID > 0)

From 63bc41556548be75ceab8fd9d1d0f5fb347d78b3 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 12 Nov 2021 18:35:42 +0900
Subject: [PATCH 05/14] Warn on suspicious types

---
 osu.sln.DotSettings | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/osu.sln.DotSettings b/osu.sln.DotSettings
index f35bdfce66..3fac94b243 100644
--- a/osu.sln.DotSettings
+++ b/osu.sln.DotSettings
@@ -209,6 +209,8 @@
 	<s:String x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=StructCanBeMadeReadOnly/@EntryIndexedValue">WARNING</s:String>
 	<s:String x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=SuggestVarOrType_005FBuiltInTypes/@EntryIndexedValue">SUGGESTION</s:String>
 	<s:String x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=SuggestVarOrType_005FSimpleTypes/@EntryIndexedValue">DO_NOT_SHOW</s:String>
+	<s:String x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=SuspiciousTypeConversion_002EGlobal/@EntryIndexedValue"></s:String>
+	<s:Boolean x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=SuspiciousTypeConversion_002EGlobal/@EntryIndexRemoved">True</s:Boolean>
 	<s:String x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=SwitchStatementMissingSomeCases/@EntryIndexedValue">DO_NOT_SHOW</s:String>
 	<s:String x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=TabsAndSpacesMismatch/@EntryIndexedValue">WARNING</s:String>
 	<s:String x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=TabsAreDisallowed/@EntryIndexedValue">WARNING</s:String>

From 1d962648c29bd3e06e2b7609698274f57256da80 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 12 Nov 2021 18:48:34 +0900
Subject: [PATCH 06/14] Standardise implementations

---
 osu.Game/Beatmaps/BeatmapInfo.cs    | 26 +++++++++++++----------
 osu.Game/Beatmaps/BeatmapSetInfo.cs | 33 +++++++++++++----------------
 osu.Game/Models/RealmBeatmap.cs     | 22 +++++++++++++++----
 osu.Game/Models/RealmBeatmapSet.cs  | 32 ++++++++++++----------------
 4 files changed, 61 insertions(+), 52 deletions(-)

diff --git a/osu.Game/Beatmaps/BeatmapInfo.cs b/osu.Game/Beatmaps/BeatmapInfo.cs
index ea2346f060..211a5f4088 100644
--- a/osu.Game/Beatmaps/BeatmapInfo.cs
+++ b/osu.Game/Beatmaps/BeatmapInfo.cs
@@ -151,25 +151,29 @@ namespace osu.Game.Beatmaps
 
         public override string ToString() => this.GetDisplayTitle();
 
-        public bool Equals(IBeatmapInfo other)
+        public bool Equals(BeatmapInfo other)
         {
-            if (other is BeatmapInfo b)
-                return Equals(b);
+            if (ReferenceEquals(this, other)) return true;
+            if (other == null) return false;
 
-            if (OnlineID > 0 && other?.OnlineID > 0)
-                return other.OnlineID == OnlineID;
+            if (ID != 0 && other.ID != 0)
+                return ID == other.ID;
 
             return false;
         }
 
-        public bool Equals(BeatmapInfo other)
+        public bool Equals(IBeatmapInfo other)
         {
-            if (ID == 0 || other?.ID == 0)
-                // one of the two BeatmapInfos we are comparing isn't sourced from a database.
-                // fall back to reference equality.
-                return ReferenceEquals(this, other);
+            if (ReferenceEquals(this, other)) return true;
+            if (other == null) return false;
 
-            return ID == other?.ID;
+            if (other is BeatmapInfo b && Equals(b))
+                return true;
+
+            if (OnlineID > 0 && other.OnlineID > 0)
+                return other.OnlineID == OnlineID;
+
+            return false;
         }
 
         public bool AudioEquals(BeatmapInfo other) => other != null && BeatmapSet != null && other.BeatmapSet != null &&
diff --git a/osu.Game/Beatmaps/BeatmapSetInfo.cs b/osu.Game/Beatmaps/BeatmapSetInfo.cs
index 5bdaf26471..51d049c8f9 100644
--- a/osu.Game/Beatmaps/BeatmapSetInfo.cs
+++ b/osu.Game/Beatmaps/BeatmapSetInfo.cs
@@ -66,32 +66,29 @@ namespace osu.Game.Beatmaps
 
         public bool Protected { get; set; }
 
-        public bool Equals(IBeatmapSetInfo other)
-        {
-            if (other is BeatmapSetInfo b)
-                return Equals(b);
-
-            if (OnlineID > 0 && other?.OnlineID > 0)
-                return other.OnlineID == OnlineID;
-
-            return false;
-        }
-
         public bool Equals(BeatmapSetInfo other)
         {
-            if (other == null)
-                return false;
+            if (ReferenceEquals(this, other)) return true;
+            if (other == null) return false;
 
             if (ID != 0 && other.ID != 0)
                 return ID == other.ID;
 
-            if (OnlineBeatmapSetID.HasValue && other.OnlineBeatmapSetID.HasValue)
-                return OnlineBeatmapSetID == other.OnlineBeatmapSetID;
+            return false;
+        }
 
-            if (!string.IsNullOrEmpty(Hash) && !string.IsNullOrEmpty(other.Hash))
-                return Hash == other.Hash;
+        public bool Equals(IBeatmapSetInfo other)
+        {
+            if (ReferenceEquals(this, other)) return true;
+            if (other == null) return false;
 
-            return ReferenceEquals(this, other);
+            if (other is BeatmapSetInfo b && Equals(b))
+                return true;
+
+            if (OnlineID > 0 && other.OnlineID > 0)
+                return other.OnlineID == OnlineID;
+
+            return false;
         }
 
         #region Implementation of IHasOnlineID
diff --git a/osu.Game/Models/RealmBeatmap.cs b/osu.Game/Models/RealmBeatmap.cs
index d1907d3ffd..f80d1f513a 100644
--- a/osu.Game/Models/RealmBeatmap.cs
+++ b/osu.Game/Models/RealmBeatmap.cs
@@ -20,7 +20,7 @@ namespace osu.Game.Models
     [ExcludeFromDynamicCompile]
     [Serializable]
     [MapTo("Beatmap")]
-    public class RealmBeatmap : RealmObject, IHasGuidPrimaryKey, IBeatmapInfo
+    public class RealmBeatmap : RealmObject, IHasGuidPrimaryKey, IBeatmapInfo, IEquatable<RealmBeatmap>
     {
         [PrimaryKey]
         public Guid ID { get; set; } = Guid.NewGuid();
@@ -98,14 +98,28 @@ namespace osu.Game.Models
 
         #endregion
 
+        public bool Equals(RealmBeatmap? other)
+        {
+            if (ReferenceEquals(this, other)) return true;
+            if (other == null) return false;
+
+            return ID == other.ID;
+        }
+
         #region Implementation of IEquatable<IBeatmapInfo>
 
         public bool Equals(IBeatmapInfo? other)
         {
-            if (other is RealmBeatmap b)
-                return b.ID == ID;
+            if (ReferenceEquals(this, other)) return true;
+            if (other == null) return false;
 
-            if (OnlineID > 0 && other?.OnlineID > 0)
+            if (other is RealmBeatmap b && Equals(b))
+                return true;
+
+            if (!string.IsNullOrEmpty(Hash) && !string.IsNullOrEmpty(other.Hash))
+                return Hash == other.Hash;
+
+            if (OnlineID > 0 && other.OnlineID > 0)
                 return other.OnlineID == OnlineID;
 
             return false;
diff --git a/osu.Game/Models/RealmBeatmapSet.cs b/osu.Game/Models/RealmBeatmapSet.cs
index 3217abb419..9cfa2de44d 100644
--- a/osu.Game/Models/RealmBeatmapSet.cs
+++ b/osu.Game/Models/RealmBeatmapSet.cs
@@ -53,32 +53,26 @@ namespace osu.Game.Models
         /// <param name="filename">The name of the file to get the storage path of.</param>
         public string? GetPathForFile(string filename) => Files.SingleOrDefault(f => string.Equals(f.Filename, filename, StringComparison.OrdinalIgnoreCase))?.File.StoragePath;
 
-        public bool Equals(IBeatmapSetInfo? other)
-        {
-            if (other is RealmBeatmapSet b)
-                return b.ID == ID;
-
-            if (OnlineID > 0 && other?.OnlineID > 0)
-                return other.OnlineID == OnlineID;
-
-            return false;
-        }
-
         public bool Equals(RealmBeatmapSet? other)
         {
-            if (other == null)
-                return false;
+            if (ReferenceEquals(this, other)) return true;
+            if (other == null) return false;
 
-            if (IsManaged && other.IsManaged)
-                return ID == other.ID;
+            return ID == other.ID;
+        }
+
+        public bool Equals(IBeatmapSetInfo? other)
+        {
+            if (ReferenceEquals(this, other)) return true;
+            if (other == null) return false;
+
+            if (other is RealmBeatmapSet b && Equals(b))
+                return true;
 
             if (OnlineID > 0 && other.OnlineID > 0)
                 return OnlineID == other.OnlineID;
 
-            if (!string.IsNullOrEmpty(Hash) && !string.IsNullOrEmpty(other.Hash))
-                return Hash == other.Hash;
-
-            return ReferenceEquals(this, other);
+            return false;
         }
 
         public override string ToString() => Metadata?.ToString() ?? base.ToString();

From a4c11e8813308b4bbd71489b711c9e556a7ca2f0 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 15 Nov 2021 14:34:50 +0900
Subject: [PATCH 07/14] Use extension method to compare online IDs

---
 osu.Game/Database/IHasOnlineID.cs      |  3 +++
 osu.Game/Extensions/ModelExtensions.cs | 29 ++++++++++++++++++++++++++
 osu.Game/Overlays/Music/Playlist.cs    |  3 ++-
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/osu.Game/Database/IHasOnlineID.cs b/osu.Game/Database/IHasOnlineID.cs
index 4e83ed8876..7a720989cd 100644
--- a/osu.Game/Database/IHasOnlineID.cs
+++ b/osu.Game/Database/IHasOnlineID.cs
@@ -1,11 +1,14 @@
 // 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;
+
 #nullable enable
 
 namespace osu.Game.Database
 {
     public interface IHasOnlineID<out T>
+        where T : IEquatable<T>
     {
         /// <summary>
         /// The server-side ID representing this instance, if one exists. Any value 0 or less denotes a missing ID (except in special cases where autoincrement is not used, like rulesets).
diff --git a/osu.Game/Extensions/ModelExtensions.cs b/osu.Game/Extensions/ModelExtensions.cs
index d8e0938d46..2545045d96 100644
--- a/osu.Game/Extensions/ModelExtensions.cs
+++ b/osu.Game/Extensions/ModelExtensions.cs
@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using osu.Game.Beatmaps;
+using osu.Game.Database;
 using osu.Game.Rulesets;
 using osu.Game.Scoring;
 using osu.Game.Users;
@@ -57,5 +58,33 @@ namespace osu.Game.Extensions
             result ??= model?.ToString() ?? @"null";
             return result;
         }
+
+        /// <summary>
+        /// Check whether the online ID of two instances match.
+        /// </summary>
+        /// <param name="instance">The instance to compare.</param>
+        /// <param name="other">The other instance to compare against.</param>
+        /// <returns>Whether online IDs match. If either instance is missing an online ID, this will return false.</returns>
+        public static bool MatchesOnlineID(this IHasOnlineID<long> instance, IHasOnlineID<long> other)
+        {
+            if (instance.OnlineID < 0 || other.OnlineID < 0)
+                return false;
+
+            return instance.OnlineID.Equals(other.OnlineID);
+        }
+
+        /// <summary>
+        /// Check whether the online ID of two instances match.
+        /// </summary>
+        /// <param name="instance">The instance to compare.</param>
+        /// <param name="other">The other instance to compare against.</param>
+        /// <returns>Whether online IDs match. If either instance is missing an online ID, this will return false.</returns>
+        public static bool MatchesOnlineID(this IHasOnlineID<int> instance, IHasOnlineID<int> other)
+        {
+            if (instance.OnlineID < 0 || other.OnlineID < 0)
+                return false;
+
+            return instance.OnlineID.Equals(other.OnlineID);
+        }
     }
 }
diff --git a/osu.Game/Overlays/Music/Playlist.cs b/osu.Game/Overlays/Music/Playlist.cs
index 4fe338926f..5de62ebfb8 100644
--- a/osu.Game/Overlays/Music/Playlist.cs
+++ b/osu.Game/Overlays/Music/Playlist.cs
@@ -7,6 +7,7 @@ using osu.Framework.Bindables;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Game.Beatmaps;
+using osu.Game.Extensions;
 using osu.Game.Graphics.Containers;
 using osuTK;
 
@@ -29,7 +30,7 @@ namespace osu.Game.Overlays.Music
             var items = (SearchContainer<RearrangeableListItem<BeatmapSetInfo>>)ListContainer;
 
             foreach (var item in items.OfType<PlaylistItem>())
-                item.InSelectedCollection = criteria.Collection?.Beatmaps.Any(b => b.BeatmapSet.Equals(item.Model)) ?? true;
+                item.InSelectedCollection = criteria.Collection?.Beatmaps.Any(b => b.MatchesOnlineID(item.Model)) ?? true;
 
             items.SearchTerm = criteria.SearchText;
         }

From 0b4822b55225bb995bff04411082cc36cf42a3a6 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 15 Nov 2021 14:35:01 +0900
Subject: [PATCH 08/14] Remove newly added equality

---
 osu.Game/Beatmaps/BeatmapInfo.cs     | 14 --------------
 osu.Game/Beatmaps/BeatmapSetInfo.cs  | 14 --------------
 osu.Game/Beatmaps/IBeatmapInfo.cs    |  3 +--
 osu.Game/Beatmaps/IBeatmapSetInfo.cs |  2 +-
 osu.Game/Models/RealmBeatmap.cs      | 21 ---------------------
 osu.Game/Models/RealmBeatmapSet.cs   | 17 ++---------------
 6 files changed, 4 insertions(+), 67 deletions(-)

diff --git a/osu.Game/Beatmaps/BeatmapInfo.cs b/osu.Game/Beatmaps/BeatmapInfo.cs
index 0b234b3c2d..6f45f5ec71 100644
--- a/osu.Game/Beatmaps/BeatmapInfo.cs
+++ b/osu.Game/Beatmaps/BeatmapInfo.cs
@@ -163,20 +163,6 @@ namespace osu.Game.Beatmaps
             return false;
         }
 
-        public bool Equals(IBeatmapInfo other)
-        {
-            if (ReferenceEquals(this, other)) return true;
-            if (other == null) return false;
-
-            if (other is BeatmapInfo b && Equals(b))
-                return true;
-
-            if (OnlineID > 0 && other.OnlineID > 0)
-                return other.OnlineID == OnlineID;
-
-            return false;
-        }
-
         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;
diff --git a/osu.Game/Beatmaps/BeatmapSetInfo.cs b/osu.Game/Beatmaps/BeatmapSetInfo.cs
index fa314fe400..6dd8cc5ade 100644
--- a/osu.Game/Beatmaps/BeatmapSetInfo.cs
+++ b/osu.Game/Beatmaps/BeatmapSetInfo.cs
@@ -78,20 +78,6 @@ namespace osu.Game.Beatmaps
             return false;
         }
 
-        public bool Equals(IBeatmapSetInfo other)
-        {
-            if (ReferenceEquals(this, other)) return true;
-            if (other == null) return false;
-
-            if (other is BeatmapSetInfo b && Equals(b))
-                return true;
-
-            if (OnlineID > 0 && other.OnlineID > 0)
-                return other.OnlineID == OnlineID;
-
-            return false;
-        }
-
         #region Implementation of IHasOnlineID
 
         int IHasOnlineID<int>.OnlineID => OnlineID ?? -1;
diff --git a/osu.Game/Beatmaps/IBeatmapInfo.cs b/osu.Game/Beatmaps/IBeatmapInfo.cs
index ab096b8897..84ea6d3019 100644
--- a/osu.Game/Beatmaps/IBeatmapInfo.cs
+++ b/osu.Game/Beatmaps/IBeatmapInfo.cs
@@ -1,7 +1,6 @@
 // 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;
 
@@ -12,7 +11,7 @@ namespace osu.Game.Beatmaps
     /// <summary>
     /// A single beatmap difficulty.
     /// </summary>
-    public interface IBeatmapInfo : IHasOnlineID<int>, IEquatable<IBeatmapInfo>
+    public interface IBeatmapInfo : IHasOnlineID<int>
     {
         /// <summary>
         /// The user-specified name given to this beatmap.
diff --git a/osu.Game/Beatmaps/IBeatmapSetInfo.cs b/osu.Game/Beatmaps/IBeatmapSetInfo.cs
index 67f38397d4..20c46d9063 100644
--- a/osu.Game/Beatmaps/IBeatmapSetInfo.cs
+++ b/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>, IEquatable<IBeatmapSetInfo>
+    public interface IBeatmapSetInfo : IHasOnlineID<int>
     {
         /// <summary>
         /// The date when this beatmap was imported.
diff --git a/osu.Game/Models/RealmBeatmap.cs b/osu.Game/Models/RealmBeatmap.cs
index f80d1f513a..2a197d296a 100644
--- a/osu.Game/Models/RealmBeatmap.cs
+++ b/osu.Game/Models/RealmBeatmap.cs
@@ -106,27 +106,6 @@ namespace osu.Game.Models
             return ID == other.ID;
         }
 
-        #region Implementation of IEquatable<IBeatmapInfo>
-
-        public bool Equals(IBeatmapInfo? other)
-        {
-            if (ReferenceEquals(this, other)) return true;
-            if (other == null) return false;
-
-            if (other is RealmBeatmap b && Equals(b))
-                return true;
-
-            if (!string.IsNullOrEmpty(Hash) && !string.IsNullOrEmpty(other.Hash))
-                return Hash == other.Hash;
-
-            if (OnlineID > 0 && other.OnlineID > 0)
-                return other.OnlineID == OnlineID;
-
-            return false;
-        }
-
-        #endregion
-
         public bool AudioEquals(RealmBeatmap? other) => other != null
                                                         && BeatmapSet != null
                                                         && other.BeatmapSet != null
diff --git a/osu.Game/Models/RealmBeatmapSet.cs b/osu.Game/Models/RealmBeatmapSet.cs
index 9cfa2de44d..1747cce67a 100644
--- a/osu.Game/Models/RealmBeatmapSet.cs
+++ b/osu.Game/Models/RealmBeatmapSet.cs
@@ -7,6 +7,7 @@ using System.Linq;
 using osu.Framework.Testing;
 using osu.Game.Beatmaps;
 using osu.Game.Database;
+using osu.Game.Extensions;
 using Realms;
 
 #nullable enable
@@ -61,21 +62,7 @@ namespace osu.Game.Models
             return ID == other.ID;
         }
 
-        public bool Equals(IBeatmapSetInfo? other)
-        {
-            if (ReferenceEquals(this, other)) return true;
-            if (other == null) return false;
-
-            if (other is RealmBeatmapSet b && Equals(b))
-                return true;
-
-            if (OnlineID > 0 && other.OnlineID > 0)
-                return OnlineID == other.OnlineID;
-
-            return false;
-        }
-
-        public override string ToString() => Metadata?.ToString() ?? base.ToString();
+        public override string ToString() => Metadata?.GetDisplayString() ?? base.ToString();
 
         IEnumerable<IBeatmapInfo> IBeatmapSetInfo.Beatmaps => Beatmaps;
 

From 18f73b985b82de1d0eb07a9e827ba53065330008 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 15 Nov 2021 14:38:01 +0900
Subject: [PATCH 09/14] Make `ModelExtensions` nullable enabled

---
 osu.Game/Extensions/ModelExtensions.cs | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/osu.Game/Extensions/ModelExtensions.cs b/osu.Game/Extensions/ModelExtensions.cs
index 2545045d96..48a3bac112 100644
--- a/osu.Game/Extensions/ModelExtensions.cs
+++ b/osu.Game/Extensions/ModelExtensions.cs
@@ -7,6 +7,8 @@ using osu.Game.Rulesets;
 using osu.Game.Scoring;
 using osu.Game.Users;
 
+#nullable enable
+
 namespace osu.Game.Extensions
 {
     public static class ModelExtensions
@@ -23,9 +25,9 @@ namespace osu.Game.Extensions
         /// extension method type inference rules cause this method to call itself and cause a stack overflow.
         /// </para>
         /// </remarks>
-        public static string GetDisplayString(this object model)
+        public static string GetDisplayString(this object? model)
         {
-            string result = null;
+            string? result = null;
 
             switch (model)
             {
@@ -65,8 +67,11 @@ namespace osu.Game.Extensions
         /// <param name="instance">The instance to compare.</param>
         /// <param name="other">The other instance to compare against.</param>
         /// <returns>Whether online IDs match. If either instance is missing an online ID, this will return false.</returns>
-        public static bool MatchesOnlineID(this IHasOnlineID<long> instance, IHasOnlineID<long> other)
+        public static bool MatchesOnlineID(this IHasOnlineID<long>? instance, IHasOnlineID<long>? other)
         {
+            if (instance == null || other == null)
+                return false;
+
             if (instance.OnlineID < 0 || other.OnlineID < 0)
                 return false;
 
@@ -79,8 +84,11 @@ namespace osu.Game.Extensions
         /// <param name="instance">The instance to compare.</param>
         /// <param name="other">The other instance to compare against.</param>
         /// <returns>Whether online IDs match. If either instance is missing an online ID, this will return false.</returns>
-        public static bool MatchesOnlineID(this IHasOnlineID<int> instance, IHasOnlineID<int> other)
+        public static bool MatchesOnlineID(this IHasOnlineID<int>? instance, IHasOnlineID<int>? other)
         {
+            if (instance == null || other == null)
+                return false;
+
             if (instance.OnlineID < 0 || other.OnlineID < 0)
                 return false;
 

From 93fe57d39970ee9c9dcc7dc0a757c2537aa10e55 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 15 Nov 2021 14:43:31 +0900
Subject: [PATCH 10/14] Update tests to match new equality not including online
 ID checks

---
 osu.Game.Tests/NonVisual/BeatmapSetInfoEqualityTest.cs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/osu.Game.Tests/NonVisual/BeatmapSetInfoEqualityTest.cs b/osu.Game.Tests/NonVisual/BeatmapSetInfoEqualityTest.cs
index 938edf07c6..534983f869 100644
--- a/osu.Game.Tests/NonVisual/BeatmapSetInfoEqualityTest.cs
+++ b/osu.Game.Tests/NonVisual/BeatmapSetInfoEqualityTest.cs
@@ -3,6 +3,7 @@
 
 using NUnit.Framework;
 using osu.Game.Beatmaps;
+using osu.Game.Extensions;
 
 namespace osu.Game.Tests.NonVisual
 {
@@ -15,7 +16,8 @@ namespace osu.Game.Tests.NonVisual
             var ourInfo = new BeatmapSetInfo { OnlineID = 123 };
             var otherInfo = new BeatmapSetInfo { OnlineID = 123 };
 
-            Assert.AreEqual(ourInfo, otherInfo);
+            Assert.AreNotEqual(ourInfo, otherInfo);
+            Assert.IsTrue(ourInfo.MatchesOnlineID(otherInfo));
         }
 
         [Test]
@@ -33,7 +35,8 @@ namespace osu.Game.Tests.NonVisual
             var ourInfo = new BeatmapSetInfo { ID = 123, OnlineID = 12 };
             var otherInfo = new BeatmapSetInfo { OnlineID = 12 };
 
-            Assert.AreEqual(ourInfo, otherInfo);
+            Assert.AreNotEqual(ourInfo, otherInfo);
+            Assert.IsTrue(ourInfo.MatchesOnlineID(otherInfo));
         }
 
         [Test]

From 285b161da73612b3ed0f4f9c189730b6483cf024 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 15 Nov 2021 14:38:14 +0900
Subject: [PATCH 11/14] Update other usages of online ID comparisons to use new
 extension method

---
 osu.Game/Online/API/Requests/Responses/APIBeatmap.cs     | 9 ++-------
 osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs  | 9 ++-------
 osu.Game/Online/API/Requests/Responses/APIUser.cs        | 3 ++-
 .../BeatmapListing/Panels/BeatmapPanelDownloadButton.cs  | 3 ++-
 osu.Game/Overlays/BeatmapSet/BeatmapPicker.cs            | 3 ++-
 osu.Game/Overlays/BeatmapSet/BeatmapRulesetTabItem.cs    | 3 ++-
 osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs | 3 ++-
 7 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs b/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
index 33098a2919..bbffaee87b 100644
--- a/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
+++ b/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
@@ -4,6 +4,7 @@
 using System;
 using Newtonsoft.Json;
 using osu.Game.Beatmaps;
+using osu.Game.Extensions;
 using osu.Game.Rulesets;
 
 #nullable enable
@@ -106,13 +107,7 @@ namespace osu.Game.Online.API.Requests.Responses
 
         #region Implementation of IEquatable<IBeatmapInfo>
 
-        public bool Equals(IBeatmapInfo? other)
-        {
-            if (OnlineID > 0 && other?.OnlineID > 0)
-                return other.OnlineID == OnlineID;
-
-            return false;
-        }
+        public bool Equals(IBeatmapInfo? other) => this.MatchesOnlineID(other);
 
         #endregion
     }
diff --git a/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs b/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
index f4515c4258..ab8287871f 100644
--- a/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
+++ b/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using Newtonsoft.Json;
 using osu.Game.Beatmaps;
 using osu.Game.Database;
+using osu.Game.Extensions;
 
 #nullable enable
 
@@ -144,13 +145,7 @@ namespace osu.Game.Online.API.Requests.Responses
 
         #region Implementation of IEquatable<IBeatmapSetInfo>
 
-        public bool Equals(IBeatmapSetInfo? other)
-        {
-            if (OnlineID > 0 && other?.OnlineID > 0)
-                return other.OnlineID == OnlineID;
-
-            return false;
-        }
+        public bool Equals(IBeatmapInfo? other) => this.MatchesOnlineID(other);
 
         #endregion
     }
diff --git a/osu.Game/Online/API/Requests/Responses/APIUser.cs b/osu.Game/Online/API/Requests/Responses/APIUser.cs
index 49edfd036b..50f5d67796 100644
--- a/osu.Game/Online/API/Requests/Responses/APIUser.cs
+++ b/osu.Game/Online/API/Requests/Responses/APIUser.cs
@@ -7,6 +7,7 @@ using System.Linq;
 using JetBrains.Annotations;
 using Newtonsoft.Json;
 using osu.Framework.Bindables;
+using osu.Game.Extensions;
 using osu.Game.Users;
 
 namespace osu.Game.Online.API.Requests.Responses
@@ -240,6 +241,6 @@ namespace osu.Game.Online.API.Requests.Responses
 
         public int OnlineID => Id;
 
-        public bool Equals(APIUser other) => OnlineID == other?.OnlineID;
+        public bool Equals(APIUser other) => this.MatchesOnlineID(other);
     }
 }
diff --git a/osu.Game/Overlays/BeatmapListing/Panels/BeatmapPanelDownloadButton.cs b/osu.Game/Overlays/BeatmapListing/Panels/BeatmapPanelDownloadButton.cs
index 8c7846783d..1282a14c3d 100644
--- a/osu.Game/Overlays/BeatmapListing/Panels/BeatmapPanelDownloadButton.cs
+++ b/osu.Game/Overlays/BeatmapListing/Panels/BeatmapPanelDownloadButton.cs
@@ -8,6 +8,7 @@ using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Game.Beatmaps;
 using osu.Game.Configuration;
+using osu.Game.Extensions;
 using osu.Game.Graphics.Containers;
 using osu.Game.Graphics.UserInterface;
 using osu.Game.Online;
@@ -80,7 +81,7 @@ namespace osu.Game.Overlays.BeatmapListing.Panels
                     case DownloadState.LocallyAvailable:
                         Predicate<BeatmapInfo> findPredicate = null;
                         if (SelectedBeatmap.Value != null)
-                            findPredicate = b => b.OnlineID == SelectedBeatmap.Value.OnlineID;
+                            findPredicate = b => b.MatchesOnlineID(SelectedBeatmap.Value);
 
                         game?.PresentBeatmap(beatmapSet, findPredicate);
                         break;
diff --git a/osu.Game/Overlays/BeatmapSet/BeatmapPicker.cs b/osu.Game/Overlays/BeatmapSet/BeatmapPicker.cs
index b152375062..59e8e8db3c 100644
--- a/osu.Game/Overlays/BeatmapSet/BeatmapPicker.cs
+++ b/osu.Game/Overlays/BeatmapSet/BeatmapPicker.cs
@@ -14,6 +14,7 @@ using osu.Framework.Graphics.Sprites;
 using osu.Framework.Input.Events;
 using osu.Game.Beatmaps;
 using osu.Game.Beatmaps.Drawables;
+using osu.Game.Extensions;
 using osu.Game.Graphics;
 using osu.Game.Graphics.Containers;
 using osu.Game.Graphics.Sprites;
@@ -166,7 +167,7 @@ namespace osu.Game.Overlays.BeatmapSet
             if (BeatmapSet != null)
             {
                 Difficulties.ChildrenEnumerable = BeatmapSet.Beatmaps
-                                                            .Where(b => b.Ruleset.OnlineID == ruleset.Value?.OnlineID)
+                                                            .Where(b => b.Ruleset.MatchesOnlineID(ruleset.Value))
                                                             .OrderBy(b => b.StarRating)
                                                             .Select(b => new DifficultySelectorButton(b)
                                                             {
diff --git a/osu.Game/Overlays/BeatmapSet/BeatmapRulesetTabItem.cs b/osu.Game/Overlays/BeatmapSet/BeatmapRulesetTabItem.cs
index b3b3d1980b..e8cdc6913b 100644
--- a/osu.Game/Overlays/BeatmapSet/BeatmapRulesetTabItem.cs
+++ b/osu.Game/Overlays/BeatmapSet/BeatmapRulesetTabItem.cs
@@ -7,6 +7,7 @@ using osu.Framework.Bindables;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Shapes;
+using osu.Game.Extensions;
 using osu.Game.Graphics;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Online.API.Requests.Responses;
@@ -64,7 +65,7 @@ namespace osu.Game.Overlays.BeatmapSet
 
             BeatmapSet.BindValueChanged(setInfo =>
             {
-                int beatmapsCount = setInfo.NewValue?.Beatmaps.Count(b => b.Ruleset.OnlineID == Value.OnlineID) ?? 0;
+                int beatmapsCount = setInfo.NewValue?.Beatmaps.Count(b => b.Ruleset.MatchesOnlineID(Value)) ?? 0;
 
                 count.Text = beatmapsCount.ToString();
                 countContainer.FadeTo(beatmapsCount > 0 ? 1 : 0);
diff --git a/osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs b/osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs
index 22537c3ce0..56863cafad 100644
--- a/osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs
+++ b/osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs
@@ -8,6 +8,7 @@ using System.Threading.Tasks;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Screens;
+using osu.Game.Extensions;
 using osu.Game.Online.Rooms;
 using osu.Game.Rulesets;
 using osu.Game.Scoring;
@@ -32,7 +33,7 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
         private void load(IBindable<RulesetInfo> ruleset)
         {
             // Sanity checks to ensure that PlaylistsPlayer matches the settings for the current PlaylistItem
-            if (Beatmap.Value.BeatmapInfo.OnlineID != PlaylistItem.Beatmap.Value.OnlineID)
+            if (!Beatmap.Value.BeatmapInfo.MatchesOnlineID(PlaylistItem.Beatmap.Value))
                 throw new InvalidOperationException("Current Beatmap does not match PlaylistItem's Beatmap");
 
             if (ruleset.Value.ID != PlaylistItem.Ruleset.Value.ID)

From 611b9fe9422e5e33ae7845b911dceda44a7b6b24 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 15 Nov 2021 14:50:09 +0900
Subject: [PATCH 12/14] Remove now unused implementations of interface equality

---
 osu.Game/Online/API/Requests/Responses/APIBeatmap.cs    | 7 -------
 osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs | 7 -------
 2 files changed, 14 deletions(-)

diff --git a/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs b/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
index bbffaee87b..2560502173 100644
--- a/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
+++ b/osu.Game/Online/API/Requests/Responses/APIBeatmap.cs
@@ -4,7 +4,6 @@
 using System;
 using Newtonsoft.Json;
 using osu.Game.Beatmaps;
-using osu.Game.Extensions;
 using osu.Game.Rulesets;
 
 #nullable enable
@@ -104,11 +103,5 @@ namespace osu.Game.Online.API.Requests.Responses
         public string Hash => throw new NotImplementedException();
 
         #endregion
-
-        #region Implementation of IEquatable<IBeatmapInfo>
-
-        public bool Equals(IBeatmapInfo? other) => this.MatchesOnlineID(other);
-
-        #endregion
     }
 }
diff --git a/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs b/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
index ab8287871f..168e9d5d51 100644
--- a/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
+++ b/osu.Game/Online/API/Requests/Responses/APIBeatmapSet.cs
@@ -6,7 +6,6 @@ using System.Collections.Generic;
 using Newtonsoft.Json;
 using osu.Game.Beatmaps;
 using osu.Game.Database;
-using osu.Game.Extensions;
 
 #nullable enable
 
@@ -142,11 +141,5 @@ namespace osu.Game.Online.API.Requests.Responses
         double IBeatmapSetInfo.MaxBPM => BPM;
 
         #endregion
-
-        #region Implementation of IEquatable<IBeatmapSetInfo>
-
-        public bool Equals(IBeatmapInfo? other) => this.MatchesOnlineID(other);
-
-        #endregion
     }
 }

From 73cb80d8a44a0c69717a47acdb2adb09da341b1a Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 15 Nov 2021 16:00:45 +0900
Subject: [PATCH 13/14] Update one more missed usage

---
 osu.Game/Screens/OnlinePlay/Lounge/Components/RoomsContainer.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/osu.Game/Screens/OnlinePlay/Lounge/Components/RoomsContainer.cs b/osu.Game/Screens/OnlinePlay/Lounge/Components/RoomsContainer.cs
index 85efdcef1a..32ae7cf859 100644
--- a/osu.Game/Screens/OnlinePlay/Lounge/Components/RoomsContainer.cs
+++ b/osu.Game/Screens/OnlinePlay/Lounge/Components/RoomsContainer.cs
@@ -82,7 +82,7 @@ namespace osu.Game.Screens.OnlinePlay.Lounge.Components
                 {
                     bool matchingFilter = true;
 
-                    matchingFilter &= r.Room.Playlist.Count == 0 || criteria.Ruleset == null || r.Room.Playlist.Any(i => i.Ruleset.Value.Equals(criteria.Ruleset));
+                    matchingFilter &= r.Room.Playlist.Count == 0 || criteria.Ruleset == null || r.Room.Playlist.Any(i => i.Ruleset.Value.MatchesOnlineID(criteria.Ruleset));
 
                     if (!string.IsNullOrEmpty(criteria.SearchString))
                         matchingFilter &= r.FilterTerms.Any(term => term.Contains(criteria.SearchString, StringComparison.InvariantCultureIgnoreCase));

From 1988b263c60331f02fd973eee2da70f077ea78df Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 15 Nov 2021 16:02:08 +0900
Subject: [PATCH 14/14] One more missed usage..

---
 osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs b/osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs
index 56863cafad..35d417520e 100644
--- a/osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs
+++ b/osu.Game/Screens/OnlinePlay/Playlists/PlaylistsPlayer.cs
@@ -36,7 +36,7 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
             if (!Beatmap.Value.BeatmapInfo.MatchesOnlineID(PlaylistItem.Beatmap.Value))
                 throw new InvalidOperationException("Current Beatmap does not match PlaylistItem's Beatmap");
 
-            if (ruleset.Value.ID != PlaylistItem.Ruleset.Value.ID)
+            if (!ruleset.Value.MatchesOnlineID(PlaylistItem.Ruleset.Value))
                 throw new InvalidOperationException("Current Ruleset does not match PlaylistItem's Ruleset");
 
             if (!PlaylistItem.RequiredMods.All(m => Mods.Value.Any(m.Equals)))