CR: Avoid "new T()" in StackObjectPool

Author: SteveSandersonMS

src/Components/Components/src/RenderTree/StackObjectPool.cs

@@ -9,16 +9,18 @@ namespace Microsoft.AspNetCore.Components.RenderTree
     // balanced as in a stack. It retains up to 'maxPreservedItems' instances in
     // memory, then for any further requests it supplies untracked instances.
 
-    internal class StackObjectPool<T> where T : class, new()
+    internal class StackObjectPool<T> where T : class
     {
         private readonly int _maxPreservedItems;
+        private readonly Func<T> _instanceFactory;
         private readonly T[] _contents;
         private int _numSuppliedItems;
         private int _numTrackedItems;
 
-        public StackObjectPool(int maxPreservedItems)
+        public StackObjectPool(int maxPreservedItems, Func<T> instanceFactory)
         {
             _maxPreservedItems = maxPreservedItems;
+            _instanceFactory = instanceFactory ?? throw new ArgumentNullException(nameof(instanceFactory));
             _contents = new T[_maxPreservedItems];
         }
 
@@ -31,7 +33,7 @@ public T Get()
                 if (_numTrackedItems < _numSuppliedItems)
                 {
                     // Need to allocate a new one
-                    var newItem = new T();
+                    var newItem = _instanceFactory();
                     _contents[_numTrackedItems++] = newItem;
                     return newItem;
                 }
@@ -44,7 +46,7 @@ public T Get()
             else
             {
                 // Pool is full; return untracked instance
-                return new T();
+                return _instanceFactory();
             }
         }
 

src/Components/Components/src/Rendering/RenderBatchBuilder.cs

@@ -31,7 +31,7 @@ internal class RenderBatchBuilder
         public Dictionary<string, int> AttributeDiffSet { get; } = new Dictionary<string, int>();
 
         internal StackObjectPool<Dictionary<object, KeyedItemInfo>> KeyedItemInfoDictionaryPool { get; }
-            = new StackObjectPool<Dictionary<object, KeyedItemInfo>>(maxPreservedItems: 10);
+            = new StackObjectPool<Dictionary<object, KeyedItemInfo>>(maxPreservedItems: 10, () => new Dictionary<object, KeyedItemInfo>());
 
         public void ClearStateForCurrentBatch()
         {

src/Components/Components/test/StackObjectPoolTest.cs

@@ -13,7 +13,7 @@ public class StackObjectPoolTest
         public void CanGetInstances()
         {
             // Arrange
-            var stackObjectPool = new StackObjectPool<object>(10);
+            var stackObjectPool = new StackObjectPool<object>(10, () => new object());
 
             // Act
             var instance1 = stackObjectPool.Get();
@@ -29,7 +29,7 @@ public void CanGetInstances()
         public void CanReturnInstances()
         {
             // Arrange
-            var stackObjectPool = new StackObjectPool<object>(10);
+            var stackObjectPool = new StackObjectPool<object>(10, () => new object());
             var instance1 = stackObjectPool.Get();
             var instance2 = stackObjectPool.Get();
 
@@ -43,7 +43,7 @@ public void CanReturnInstances()
         public void ReusesInstancesInPoolUpToCapacity()
         {
             // Arrange
-            var stackObjectPool = new StackObjectPool<object>(10);
+            var stackObjectPool = new StackObjectPool<object>(10, () => new object());
             var instance1 = stackObjectPool.Get();
             var instance2 = stackObjectPool.Get();
             stackObjectPool.Return(instance2);
@@ -66,7 +66,7 @@ public void ReusesInstancesInPoolUpToCapacity()
         public void SuppliesTransientInstancesWhenExceedingCapacity()
         {
             // Arrange
-            var stackObjectPool = new StackObjectPool<object>(1);
+            var stackObjectPool = new StackObjectPool<object>(1, () => new object());
 
             // Act 1: Returns distinct instances beyond capacity
             var instance1 = stackObjectPool.Get();
@@ -94,7 +94,7 @@ public void SuppliesTransientInstancesWhenExceedingCapacity()
         public void CannotReturnWhenEmpty()
         {
             // Arrange
-            var stackObjectPool = new StackObjectPool<object>(10);
+            var stackObjectPool = new StackObjectPool<object>(10, () => new object());
 
             // Act/Assert
             var ex = Assert.Throws<InvalidOperationException>(() =>
@@ -108,7 +108,7 @@ public void CannotReturnWhenEmpty()
         public void CannotReturnMismatchingTrackedItem()
         {
             // Arrange
-            var stackObjectPool = new StackObjectPool<object>(10);
+            var stackObjectPool = new StackObjectPool<object>(10, () => new object());
             var instance1 = stackObjectPool.Get();
             var instance2 = stackObjectPool.Get();