Add IBeatmap<T> interface for typed hitobject retrieval

osu.Game/Beatmaps/Beatmap.cs

@@ -14,7 +14,7 @@ namespace osu.Game.Beatmaps
     /// <summary>
     /// A Beatmap containing converted HitObjects.
     /// </summary>
-    public class Beatmap<T> : IBeatmap
+    public class Beatmap<T> : IBeatmap<T>
         where T : HitObject
     {
         public BeatmapInfo BeatmapInfo { get; set; } = new BeatmapInfo
@@ -36,17 +36,13 @@ public class Beatmap<T> : IBeatmap
 
         public List<BreakPeriod> Breaks { get; set; } = new List<BreakPeriod>();
 
-        /// <summary>
-        /// Total amount of break time in the beatmap.
-        /// </summary>
         [JsonIgnore]
         public double TotalBreakTime => Breaks.Sum(b => b.Duration);
 
-        /// <summary>
-        /// The HitObjects this Beatmap contains.
-        /// </summary>
         [JsonConverter(typeof(TypedListConverter<HitObject>))]
-        public List<T> HitObjects = new List<T>();
+        public List<T> HitObjects { get; set; } = new List<T>();
+
+        IReadOnlyList<T> IBeatmap<T>.HitObjects => HitObjects;
 
         IReadOnlyList<HitObject> IBeatmap.HitObjects => HitObjects;
 

osu.Game/Beatmaps/IBeatmap.cs

@@ -53,4 +53,13 @@ public interface IBeatmap : IJsonSerializable
         /// <returns>The shallow-cloned beatmap.</returns>
         IBeatmap Clone();
     }
+
+    public interface IBeatmap<out T> : IBeatmap
+        where T : HitObject
+    {
+        /// <summary>
+        /// The hitobjects contained by this beatmap.
+        /// </summary>
+        new IReadOnlyList<T> HitObjects { get; }
+    }
 }