Don't deep-clone beatmapinfo/control points

osu.Game.Rulesets.Taiko/Beatmaps/TaikoBeatmapConverter.cs

@@ -8,7 +8,6 @@ using osu.Game.Rulesets.Taiko.Objects;
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using osu.Game.IO.Serialization;
 using osu.Game.Audio;
 using osu.Game.Beatmaps.ControlPoints;
 
@@ -51,8 +50,9 @@ namespace osu.Game.Rulesets.Taiko.Beatmaps
         protected override Beatmap<TaikoHitObject> ConvertBeatmap(IBeatmap original)
         {
             // Rewrite the beatmap info to add the slider velocity multiplier
-            BeatmapInfo info = original.BeatmapInfo.DeepClone();
+            original.BeatmapInfo = original.BeatmapInfo.Clone();
-            info.BaseDifficulty.SliderMultiplier *= legacy_velocity_multiplier;
+            original.BeatmapInfo.BaseDifficulty = original.BeatmapInfo.BaseDifficulty.Clone();
+            original.BeatmapInfo.BaseDifficulty.SliderMultiplier *= legacy_velocity_multiplier;
 
             Beatmap<TaikoHitObject> converted = base.ConvertBeatmap(original);
 

osu.Game/Beatmaps/Beatmap.cs

@@ -6,7 +6,6 @@ using osu.Game.Rulesets.Objects;
 using System.Collections.Generic;
 using System.Linq;
 using osu.Game.Beatmaps.ControlPoints;
-using osu.Game.IO.Serialization;
 using Newtonsoft.Json;
 using osu.Game.IO.Serialization.Converters;
 
@@ -55,17 +54,11 @@ namespace osu.Game.Beatmaps
 
         IBeatmap IBeatmap.Clone() => Clone();
 
-        public Beatmap<T> Clone()
+        public Beatmap<T> Clone() => (Beatmap<T>)MemberwiseClone();
-        {
-            var newInstance = (Beatmap<T>)MemberwiseClone();
-            newInstance.BeatmapInfo = BeatmapInfo.DeepClone();
-
-            return newInstance;
-        }
     }
 
     public class Beatmap : Beatmap<HitObject>
     {
-        public Beatmap Clone() => (Beatmap)base.Clone();
+        public new Beatmap Clone() => (Beatmap)base.Clone();
     }
 }

osu.Game/Beatmaps/BeatmapConverter.cs

@@ -53,8 +53,6 @@ namespace osu.Game.Beatmaps
         {
             var beatmap = CreateBeatmap();
 
-            // todo: this *must* share logic (or directly use) Beatmap<T>'s constructor.
-            // right now this isn't easily possible due to generic entanglement.
             beatmap.BeatmapInfo = original.BeatmapInfo;
             beatmap.ControlPointInfo = original.ControlPointInfo;
             beatmap.HitObjects = original.HitObjects.SelectMany(h => convert(h, original)).ToList();

osu.Game/Beatmaps/BeatmapDifficulty.cs

@@ -32,6 +32,11 @@ namespace osu.Game.Beatmaps
         public double SliderMultiplier { get; set; } = 1;
         public double SliderTickRate { get; set; } = 1;
 
+        /// <summary>
+        /// Returns a shallow-clone of this <see cref="BeatmapDifficulty"/>.
+        /// </summary>
+        public BeatmapDifficulty Clone() => (BeatmapDifficulty)MemberwiseClone();
+
         /// <summary>
         /// Maps a difficulty value [0, 10] to a two-piece linear range of values.
         /// </summary>

osu.Game/Beatmaps/BeatmapInfo.cs

@@ -143,5 +143,10 @@ namespace osu.Game.Beatmaps
         public bool BackgroundEquals(BeatmapInfo other) => other != null && BeatmapSet != null && other.BeatmapSet != null &&
                                                       BeatmapSet.Hash == other.BeatmapSet.Hash &&
                                                       (Metadata ?? BeatmapSet.Metadata).BackgroundFile == (other.Metadata ?? other.BeatmapSet.Metadata).BackgroundFile;
+
+        /// <summary>
+        /// Returns a shallow-clone of this <see cref="BeatmapInfo"/>.
+        /// </summary>
+        public BeatmapInfo Clone() => (BeatmapInfo)MemberwiseClone();
     }
 }

osu.Game/IO/Serialization/IJsonSerializable.cs

@@ -18,8 +18,6 @@ namespace osu.Game.IO.Serialization
 
         public static void DeserializeInto<T>(this string objString, T target) => JsonConvert.PopulateObject(objString, target, CreateGlobalSettings());
 
-        public static T DeepClone<T>(this T obj) where T : IJsonSerializable => Deserialize<T>(Serialize(obj));
-
         /// <summary>
         /// Creates the default <see cref="JsonSerializerSettings"/> that should be used for all <see cref="IJsonSerializable"/>s.
         /// </summary>

osu.Game/Rulesets/UI/Scrolling/ScrollingRulesetContainer.cs

@@ -8,7 +8,6 @@ using osu.Framework.Extensions.IEnumerableExtensions;
 using osu.Framework.Lists;
 using osu.Game.Beatmaps;
 using osu.Game.Beatmaps.ControlPoints;
-using osu.Game.IO.Serialization;
 using osu.Game.Rulesets.Objects;
 using osu.Game.Rulesets.Objects.Types;
 using osu.Game.Rulesets.Timing;
@@ -104,7 +103,7 @@ namespace osu.Game.Rulesets.UI.Scrolling
             if (index < 0)
                 return new MultiplierControlPoint(time);
 
-            return new MultiplierControlPoint(time, DefaultControlPoints[index].DeepClone());
+            return new MultiplierControlPoint(time, DefaultControlPoints[index]);
         }
     }
 }