⚡ Optimize list instantiation in EventBus.Subscribe

src/GameUtils/Entity/EventBus.cs

@@ -18,11 +18,16 @@ public void Subscribe<TEvent>(Action<TEvent> handler)
         var type = typeof(TEvent);
 
         ref var listObj = ref System.Runtime.InteropServices.CollectionsMarshal.GetValueRefOrAddDefault(_handlers, type, out bool exists);
+        List<Action<TEvent>> list;
         if (!exists)
         {
-            listObj = new List<Action<TEvent>>();
+            list = new List<Action<TEvent>>();
+            listObj = list;
+        }
+        else
+        {
+            list = (List<Action<TEvent>>)listObj!;
         }
-        var list = (List<Action<TEvent>>)listObj!;
         list.Add(handler);
         _snapshots.Remove(type);
     }

tests/GameUtils.Benchmarks/EventBusBenchmarks.cs

@@ -0,0 +1,42 @@
+using BenchmarkDotNet.Attributes;
+using GameUtils.Entity;
+using System;
+
+namespace GameUtils.Benchmarks
+{
+    [MemoryDiagnoser]
+    public class EventBusBenchmarks
+    {
+        private class TestEvent1 { }
+        private class TestEvent2 { }
+
+        private Action<TestEvent1> _handler1 = null!;
+        private Action<TestEvent2> _handler2 = null!;
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            _handler1 = e => { };
+            _handler2 = e => { };
+        }
+
+        [Benchmark]
+        public void SubscribeNewEvent()
+        {
+            var bus = new EventBus();
+            bus.Subscribe(_handler1);
+            bus.Subscribe(_handler2);
+        }
+
+        [Benchmark]
+        public void SubscribeExistingEvent()
+        {
+            var bus = new EventBus();
+            bus.Subscribe(_handler1);
+            for (int i = 0; i < 100; i++)
+            {
+                bus.Subscribe(_handler1);
+            }
+        }
+    }
+}