Optimise by removing state machine

osu.Game.Rulesets.Osu/UI/OrderedHitPolicy.cs

@@ -1,7 +1,9 @@
 // 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.Collections;
 using System.Collections.Generic;
+using System.Diagnostics;
 using osu.Game.Rulesets.Objects;
 using osu.Game.Rulesets.Objects.Drawables;
 using osu.Game.Rulesets.Osu.Objects.Drawables;
@@ -36,11 +38,14 @@ namespace osu.Game.Rulesets.Osu.UI
         {
             DrawableHitObject blockingObject = null;
 
-            // Find the last hitobject which blocks future hits.
-            foreach (var obj in enumerateHitObjectsUpTo(hitObject))
+            var enumerator = new HitObjectEnumerator(hitObjectContainer, hitObject.HitObject.StartTime);
+
+            while (enumerator.MoveNext())
             {
-                if (hitObjectCanBlockFutureHits(obj))
-                    blockingObject = obj;
+                Debug.Assert(enumerator.Current != null);
+
+                if (hitObjectCanBlockFutureHits(enumerator.Current))
+                    blockingObject = enumerator.Current;
             }
 
             // If there is no previous hitobject, allow the hit.
@@ -67,13 +72,17 @@ namespace osu.Game.Rulesets.Osu.UI
             if (!hitObjectCanBlockFutureHits(hitObject))
                 return;
 
-            foreach (var obj in enumerateHitObjectsUpTo(hitObject))
+            var enumerator = new HitObjectEnumerator(hitObjectContainer, hitObject.HitObject.StartTime);
+
+            while (enumerator.MoveNext())
             {
-                if (obj.Judged)
+                Debug.Assert(enumerator.Current != null);
+
+                if (enumerator.Current.Judged)
                     continue;
 
-                if (hitObjectCanBlockFutureHits(obj))
-                    ((DrawableOsuHitObject)obj).MissForcefully();
+                if (hitObjectCanBlockFutureHits(enumerator.Current))
+                    ((DrawableOsuHitObject)enumerator.Current).MissForcefully();
             }
         }
 
@@ -84,23 +93,89 @@ namespace osu.Game.Rulesets.Osu.UI
         private static bool hitObjectCanBlockFutureHits(DrawableHitObject hitObject)
             => hitObject is DrawableHitCircle;
 
-        // Todo: Inefficient
-        private IEnumerable<DrawableHitObject> enumerateHitObjectsUpTo(DrawableHitObject hitObject)
+        private struct HitObjectEnumerator : IEnumerator<DrawableHitObject>
         {
-            return enumerate(hitObjectContainer.AliveObjects);
+            private readonly IEnumerator<DrawableHitObject> hitObjectEnumerator;
+            private readonly double targetTime;
 
-            IEnumerable<DrawableHitObject> enumerate(IEnumerable<DrawableHitObject> list)
+            private DrawableHitObject currentTopLevel;
+            private int currentNestedIndex;
+
+            public HitObjectEnumerator(HitObjectContainer hitObjectContainer, double targetTime)
             {
-                foreach (var obj in list)
-                {
-                    if (obj.HitObject.StartTime >= hitObject.HitObject.StartTime)
-                        yield break;
+                hitObjectEnumerator = hitObjectContainer.AliveObjects.GetEnumerator();
+                this.targetTime = targetTime;
 
-                    yield return obj;
+                currentTopLevel = null;
+                currentNestedIndex = -1;
+                Current = null;
+            }
 
-                    foreach (var nested in enumerate(obj.NestedHitObjects))
-                        yield return nested;
-                }
+            /// <summary>
+            /// Attempts to move to the next top-level or nested hitobject.
+            /// Stops when no such hitobject is found or until the hitobject start time reaches <see cref="targetTime"/>.
+            /// </summary>
+            /// <returns>Whether a new hitobject was moved to.</returns>
+            public bool MoveNext()
+            {
+                // If we don't already have a top-level hitobject, try to get one.
+                if (currentTopLevel == null)
+                    return moveNextTopLevel();
+
+                // If we have a top-level hitobject, try to move to the next nested hitobject or otherwise move to the next top-level hitobject.
+                if (!moveNextNested())
+                    return moveNextTopLevel();
+
+                // Guaranteed by moveNextNested() to have a hitobject.
+                return true;
+            }
+
+            /// <summary>
+            /// Attempts to move to the next top-level hitobject.
+            /// </summary>
+            /// <returns>Whether a new top-level hitobject was found.</returns>
+            private bool moveNextTopLevel()
+            {
+                currentNestedIndex = -1;
+
+                hitObjectEnumerator.MoveNext();
+                currentTopLevel = hitObjectEnumerator.Current;
+
+                Current = currentTopLevel;
+
+                return Current?.HitObject.StartTime < targetTime;
+            }
+
+            /// <summary>
+            /// Attempts to move to the next nested hitobject in the current top-level hitobject.
+            /// </summary>
+            /// <returns>Whether a new nested hitobject was moved to.</returns>
+            private bool moveNextNested()
+            {
+                currentNestedIndex++;
+                if (currentNestedIndex >= currentTopLevel.NestedHitObjects.Count)
+                    return false;
+
+                Current = currentTopLevel.NestedHitObjects[currentNestedIndex];
+                Debug.Assert(Current != null);
+
+                return Current?.HitObject.StartTime < targetTime;
+            }
+
+            public void Reset()
+            {
+                hitObjectEnumerator.Reset();
+                currentTopLevel = null;
+                currentNestedIndex = -1;
+                Current = null;
+            }
+
+            public DrawableHitObject Current { get; set; }
+
+            object IEnumerator.Current => Current;
+
+            public void Dispose()
+            {
             }
         }
     }