TechTree.GatherOwnedPrerequisites performance improvements.

- Consuming methods cared only about the count and not the actual actors, so only counts the actors rather that creating lists.
- ProvidesPrerequisites implementations return cached objects rather then allocating new enumerables on each call.

OpenRA.Mods.Cnc/Traits/SupportPowers/GrantPrerequisiteChargeDrainPower.cs

@@ -43,6 +43,7 @@ namespace OpenRA.Mods.Cnc.Traits
 	public class GrantPrerequisiteChargeDrainPower : SupportPower, ITechTreePrerequisite, INotifyOwnerChanged
 	{
 		readonly GrantPrerequisiteChargeDrainPowerInfo info;
+		readonly string[] prerequisites;
 		TechTree techTree;
 		bool active;
 
@@ -50,6 +51,7 @@ namespace OpenRA.Mods.Cnc.Traits
 			: base(self, info)
 		{
 			this.info = info;
+			prerequisites = new[] { info.Prerequisite };
 		}
 
 		protected override void Created(Actor self)
@@ -82,16 +84,7 @@ namespace OpenRA.Mods.Cnc.Traits
 			techTree.ActorChanged(self);
 		}
 
-		IEnumerable<string> ITechTreePrerequisite.ProvidesPrerequisites
+		IEnumerable<string> ITechTreePrerequisite.ProvidesPrerequisites => active ? prerequisites : Enumerable.Empty<string>();
-		{
-			get
-			{
-				if (!active)
-					yield break;
-
-				yield return info.Prerequisite;
-			}
-		}
 
 		public class DischargeableSupportPowerInstance : SupportPowerInstance
 		{

OpenRA.Mods.Common/Traits/Player/ProvidesPrerequisite.cs

@@ -11,6 +11,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
@@ -39,7 +40,7 @@ namespace OpenRA.Mods.Common.Traits
 
 	public class ProvidesPrerequisite : ConditionalTrait<ProvidesPrerequisiteInfo>, ITechTreePrerequisite, INotifyOwnerChanged, INotifyCreated
 	{
-		readonly string prerequisite;
+		readonly string[] prerequisites;
 
 		bool enabled;
 		TechTree techTree;
@@ -48,24 +49,15 @@ namespace OpenRA.Mods.Common.Traits
 		public ProvidesPrerequisite(ActorInitializer init, ProvidesPrerequisiteInfo info)
 			: base(info)
 		{
-			prerequisite = info.Prerequisite;
+			if (string.IsNullOrEmpty(info.Prerequisite))
-
+				prerequisites = new[] { init.Self.Info.Name };
-			if (string.IsNullOrEmpty(prerequisite))
+			else
-				prerequisite = init.Self.Info.Name;
+				prerequisites = new[] { info.Prerequisite };
 
 			faction = init.GetValue<FactionInit, string>(init.Self.Owner.Faction.InternalName);
 		}
 
-		public IEnumerable<string> ProvidesPrerequisites
+		public IEnumerable<string> ProvidesPrerequisites => enabled ? prerequisites : Enumerable.Empty<string>();
-		{
-			get
-			{
-				if (!enabled)
-					yield break;
-
-				yield return prerequisite;
-			}
-		}
 
 		protected override void Created(Actor self)
 		{

OpenRA.Mods.Common/Traits/Player/ProvidesTechPrerequisite.cs

@@ -11,6 +11,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
@@ -38,11 +39,9 @@ namespace OpenRA.Mods.Common.Traits
 		readonly ProvidesTechPrerequisiteInfo info;
 		readonly bool enabled;
 
-		static readonly string[] NoPrerequisites = Array.Empty<string>();
-
 		public string Name => info.Name;
 
-		public IEnumerable<string> ProvidesPrerequisites => enabled ? info.Prerequisites : NoPrerequisites;
+		public IEnumerable<string> ProvidesPrerequisites => enabled ? info.Prerequisites : Enumerable.Empty<string>();
 
 		public ProvidesTechPrerequisite(ProvidesTechPrerequisiteInfo info, ActorInitializer init)
 		{

OpenRA.Mods.Common/Traits/Player/TechTree.cs

@@ -12,7 +12,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using OpenRA.Primitives;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
@@ -71,9 +70,9 @@ namespace OpenRA.Mods.Common.Traits
 					^ !ownedPrereqs.ContainsKey(p.Replace("!", "").Replace("~", ""))));
 		}
 
-		static Cache<string, List<Actor>> GatherOwnedPrerequisites(Player player)
+		static Dictionary<string, int> GatherOwnedPrerequisites(Player player)
 		{
-			var ret = new Cache<string, List<Actor>>(x => new List<Actor>());
+			var ret = new Dictionary<string, int>();
 			if (player == null)
 				return ret;
 
@@ -89,7 +88,8 @@ namespace OpenRA.Mods.Common.Traits
 					if (p == null)
 						continue;
 
-					ret[p].Add(b.Actor);
+					ret.TryGetValue(p, out var count);
+					ret[p] = count + 1;
 				}
 			}
 
@@ -103,7 +103,11 @@ namespace OpenRA.Mods.Common.Traits
 					a.Actor.Info.TraitInfo<BuildableInfo>().BuildLimit > 0);
 
 			foreach (var buildable in buildables)
-				ret[buildable.Actor.Info.Name].Add(buildable.Actor);
+			{
+				var name = buildable.Actor.Info.Name;
+				ret.TryGetValue(name, out var count);
+				ret[name] = count + 1;
+			}
 
 			return ret;
 		}
@@ -132,7 +136,7 @@ namespace OpenRA.Mods.Common.Traits
 				hidden = false;
 			}
 
-			bool HasPrerequisites(Cache<string, List<Actor>> ownedPrerequisites)
+			bool HasPrerequisites(Dictionary<string, int> ownedPrerequisites)
 			{
 				// PERF: Avoid LINQ.
 				foreach (var prereq in prerequisites)
@@ -145,7 +149,7 @@ namespace OpenRA.Mods.Common.Traits
 				return true;
 			}
 
-			bool IsHidden(Cache<string, List<Actor>> ownedPrerequisites)
+			bool IsHidden(Dictionary<string, int> ownedPrerequisites)
 			{
 				// PERF: Avoid LINQ.
 				foreach (var prereq in prerequisites)
@@ -160,12 +164,12 @@ namespace OpenRA.Mods.Common.Traits
 				return false;
 			}
 
-			public void Update(Cache<string, List<Actor>> ownedPrerequisites)
+			public void Update(Dictionary<string, int> ownedPrerequisites)
 			{
-				var hasReachedLimit = limit > 0 && ownedPrerequisites.ContainsKey(Key) && ownedPrerequisites[Key].Count >= limit;
+				var hasReachedLimit = limit > 0 && ownedPrerequisites.TryGetValue(Key, out var count) && count >= limit;
 
 				// The '!' annotation inverts prerequisites: "I'm buildable if this prerequisite *isn't* met"
-				var nowHasPrerequisites = HasPrerequisites(ownedPrerequisites) && !hasReachedLimit;
+				var nowHasPrerequisites = !hasReachedLimit && HasPrerequisites(ownedPrerequisites);
 				var nowHidden = IsHidden(ownedPrerequisites);
 
 				if (initialized == false)