From fbf4be340e89a07b2258a5583605a60eb09a2dda Mon Sep 17 00:00:00 2001
From: NathanKell <nathankell@gmail.com>
Date: Mon, 4 Dec 2023 01:55:26 -0800
Subject: [PATCH] Add CachedObject<T> and ResettableCachedObject<T> which I
 wrote for Kerbalism. A simple object cache to lower GC overhead.

---
 Source/ROUtils/CachedObject.cs | 113 +++++++++++++++++++++++++++++++++
 Source/ROUtils/ROUtils.csproj  |   1 +
 2 files changed, 114 insertions(+)
 create mode 100644 Source/ROUtils/CachedObject.cs

diff --git a/Source/ROUtils/CachedObject.cs b/Source/ROUtils/CachedObject.cs
new file mode 100644
index 0000000..264b99f
--- /dev/null
+++ b/Source/ROUtils/CachedObject.cs
@@ -0,0 +1,113 @@
+using UnityEngine;
+using System.Collections.Generic;
+using System;
+
+namespace ROUtils
+{
+    /// <summary>
+    /// This lets us use CachedObject<T> to
+    /// avoid retyping the caching code
+    /// </summary>
+    public interface IResettable
+    {
+        void Reset();
+    }
+
+    /// <summary>
+    /// A simple object cache, will support any class
+    /// with a parameterless constructor
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    public class CachedObject<T> where T : class, new()
+    {
+        protected List<T> objects = new List<T>();
+        protected int active = 0;
+
+        /// <summary>
+        /// Returns a new T from the cache or, if there aren't
+        /// any free, creates a new one and adds it to the cache
+        /// </summary>
+        /// <returns></returns>
+        public T Next()
+        {
+            if (active < objects.Count)
+                return objects[active++];
+
+            var next = new T();
+            ++active;
+            objects.Add(next);
+            return next;
+        }
+
+        /// <summary>
+        /// Frees an object, returning it to the cache
+        /// and compacting the active set
+        /// </summary>
+        /// <param name="obj"></param>
+        /// <returns>true if the object is found in the cache</returns>
+        public bool Free(T obj)
+        {
+            for (int i = active; i-- > 0;)
+            {
+                var o = objects[i];
+                if (o == obj)
+                {
+                    --active;
+                    objects[i] = objects[active];
+                    objects[active] = obj;
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Fully clears the cache. This will expose the objects to GC!
+        /// </summary>
+        public void Clear()
+        {
+            objects.Clear();
+            active = 0;
+        }
+    }
+
+    /// <summary>
+    /// A simple object cache, will support any class with
+    /// a parameterless constructor that implements IResettable.
+    /// It will reset objects when freeing them, and adds the Reset
+    /// method that resets all objects but leaves them in the cache
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    public class ResettableCachedObject<T> : CachedObject<T> where T : class, IResettable, new()
+    {
+        /// <summary>
+        /// Frees an object, resetting it, returning it
+        /// to the cache, and compacting the active set
+        /// </summary>
+        /// <param name="obj"></param>
+        /// <returns>true if the object is found in the cache</returns>
+        public new bool Free(T obj)
+        {
+            if (base.Free(obj))
+            {
+                obj.Reset();
+                return true;
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Resets all objects in the cache and
+        /// makes them all available
+        /// </summary>
+        public void Reset()
+        {
+            for (int i = active; i-- > 0;)
+                objects[i].Reset();
+
+            active = 0;
+        }
+    }
+}
diff --git a/Source/ROUtils/ROUtils.csproj b/Source/ROUtils/ROUtils.csproj
index d5d5ec1..c916fd8 100644
--- a/Source/ROUtils/ROUtils.csproj
+++ b/Source/ROUtils/ROUtils.csproj
@@ -124,6 +124,7 @@
     <Compile Include="DataTypes\PersistentSortedList.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="ResourceUnitInfo.cs" />
+    <Compile Include="CachedObject.cs" />
     <Compile Include="SingletonHost.cs" />
     <Compile Include="Utils\ContinuousLogger.cs" />
     <Compile Include="Utils\DTUtils.cs" />