Updated with improved nullable support.

Author: Oren (electricessence)

source/.editorconfig

@@ -0,0 +1,10 @@
+[*.cs]
+
+# CA1707: Identifiers should not contain underscores
+dotnet_diagnostic.CA1707.severity = silent
+
+# CA1303: Do not pass literals as localized parameters
+dotnet_diagnostic.CA1303.severity = silent
+
+# CA1051: Do not declare visible instance fields
+dotnet_diagnostic.CA1051.severity = silent

source/Array/InterlockedArrayObjectPool.cs

@@ -14,7 +14,7 @@ public class InterlockedArrayObjectPool<T> : ObjectPoolBase<T>
 		where T : class
 	{
 
-		public InterlockedArrayObjectPool(Func<T> factory, Action<T> recycler, Action<T> disposer, int capacity = DEFAULT_CAPACITY)
+		public InterlockedArrayObjectPool(Func<T> factory, Action<T>? recycler, Action<T>? disposer, int capacity = DEFAULT_CAPACITY)
 			: base(factory, recycler, disposer, capacity)
 		{
 			Pool = new ReferenceContainer<T>[capacity - 1];
@@ -33,6 +33,7 @@ public InterlockedArrayObjectPool(Func<T> factory, int capacity = DEFAULT_CAPACI
 		public override int Count
 			=> Pool.Count(e => e.Value != null) + PocketCount;
 
+		[System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1062:Validate arguments of public methods", Justification = "Should never be null.")]
 		protected virtual bool Store(ReferenceContainer<T>[] p, T item, int index)
 			=> p[index].TrySave(item);
 
@@ -43,7 +44,7 @@ protected override bool Receive(T item)
 
 			for (var i = 0; i < len; i++)
 			{
-				if (Store(elements, item, i))
+				if (Store(elements!, item, i))
 				{
 					var m = MaxStored;
 					if (i >= m) Interlocked.CompareExchange(ref MaxStored, m + MaxStoredIncrement, m);
@@ -55,7 +56,7 @@ protected override bool Receive(T item)
 			return false;
 		}
 
-		protected override T TryRelease()
+		protected override T? TryRelease()
 		{
 			// We missed getting the first item or it wasn't there.
 			var elements = Pool;
@@ -74,7 +75,7 @@ protected override T TryRelease()
 		protected override void OnDispose()
 		{
 			base.OnDispose();
-			Pool = null;
+			Pool = null!;
 			MaxStored = 0;
 		}
 

source/Array/OptimisticArrayObjectPool.cs

@@ -12,7 +12,7 @@ public class OptimisticArrayObjectPool<T> : InterlockedArrayObjectPool<T>
 		where T : class
 	{
 
-		public OptimisticArrayObjectPool(Func<T> factory, Action<T> recycler, int capacity = DEFAULT_CAPACITY)
+		public OptimisticArrayObjectPool(Func<T> factory, Action<T>? recycler, int capacity = DEFAULT_CAPACITY)
 			: base(factory, recycler, null /* disposer not applicable here */, capacity)
 		{ }
 
@@ -25,6 +25,7 @@ protected override bool SaveToPocket(T item)
 			=> Pocket.SetIfNull(item);
 
 		// As suggested by Roslyn's implementation, don't worry about interlocking here.  It's okay if a few get loose.
+		[System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1062:Validate arguments of public methods", Justification = "Should never be null.")]
 		protected override bool Store(ReferenceContainer<T>[] p, T item, int index)
 			=> p[index].SetIfNull(item);
 	}

source/Collection/CollectionWrapperObjectPool.cs

@@ -8,7 +8,7 @@ public class CollectionWrapperObjectPool<T, TCollection> : TrimmableGenericColle
 		where T : class
 		where TCollection : class, ICollection<T>
 	{
-		public CollectionWrapperObjectPool(TCollection pool, Func<T> factory, Action<T> recycler, Action<T> disposer, int capacity = DEFAULT_CAPACITY, bool countTrackingEnabled = true)
+		public CollectionWrapperObjectPool(TCollection pool, Func<T> factory, Action<T>? recycler, Action<T>? disposer, int capacity = DEFAULT_CAPACITY, bool countTrackingEnabled = true)
 			: base(pool, factory, recycler, disposer, capacity, countTrackingEnabled)
 		{
 		}
@@ -35,9 +35,9 @@ protected override bool Receive(T item)
 			return false;
 		}
 
-		protected override T TryRelease()
+		protected override T? TryRelease()
 		{
-			retry:
+		retry:
 
 			var p = Pool;
 			var item = p?.FirstOrDefault();
@@ -47,7 +47,7 @@ protected override T TryRelease()
 				 * This implementation is in place for reference more than practice.  Sub classes should override. */
 
 			bool wasRemoved;
-			lock (p) wasRemoved = p.Remove(item);
+			lock (p!) wasRemoved = p.Remove(item);
 			if (!wasRemoved) goto retry;
 
 			return item;

source/Collection/ConcurrentQueueObjectPool.cs

@@ -7,7 +7,7 @@ public sealed class ConcurrentQueueObjectPool<T> : TrimmableCollectionObjectPool
 		where T : class
 	{
 
-		public ConcurrentQueueObjectPool(Func<T> factory, Action<T> recycler, Action<T> disposer, int capacity = DEFAULT_CAPACITY)
+		public ConcurrentQueueObjectPool(Func<T> factory, Action<T>? recycler, Action<T>? disposer, int capacity = DEFAULT_CAPACITY)
 			: base(new ConcurrentQueue<T>(), factory, recycler, disposer, capacity)
 		{
 		}
@@ -31,7 +31,7 @@ protected override bool Receive(T item)
 			return true;
 		}
 
-		protected override T TryRelease()
+		protected override T? TryRelease()
 		{
 			var p = Pool;
 			if (p == null) return null;

source/Collection/ConcurrentStackObjectPool.cs

@@ -7,7 +7,7 @@ public sealed class ConcurrentStackObjectPool<T> : TrimmableCollectionObjectPool
 		where T : class
 	{
 
-		public ConcurrentStackObjectPool(Func<T> factory, Action<T> recycler, Action<T> disposer, int capacity = DEFAULT_CAPACITY)
+		public ConcurrentStackObjectPool(Func<T> factory, Action<T>? recycler, Action<T>? disposer, int capacity = DEFAULT_CAPACITY)
 			: base(new ConcurrentStack<T>(), factory, recycler, disposer, capacity)
 		{
 		}
@@ -26,7 +26,7 @@ protected override bool Receive(T item)
 			return true;
 		}
 
-		protected override T TryRelease()
+		protected override T? TryRelease()
 		{
 			var p = Pool;
 			if (p == null) return null;

source/Collection/QueueObjectPool.cs

@@ -7,7 +7,7 @@ public sealed class QueueObjectPool<T> : TrimmableCollectionObjectPoolBase<T, Qu
 		where T : class
 	{
 
-		public QueueObjectPool(Func<T> factory, Action<T> recycler, Action<T> disposer, int capacity = DEFAULT_CAPACITY)
+		public QueueObjectPool(Func<T> factory, Action<T>? recycler, Action<T>? disposer, int capacity = DEFAULT_CAPACITY)
 			: base(
 				  new Queue<T>(Math.Min(DEFAULT_CAPACITY, capacity)) /* Very very slight speed improvment when capacity is initially set. */,
 				  factory, recycler, disposer, capacity, false)
@@ -34,7 +34,7 @@ protected override bool Receive(T item)
 			return false;
 		}
 
-		protected override T TryRelease()
+		protected override T? TryRelease()
 		{
 			var p = Pool;
 			if (p != null && p.Count != 0)

source/Collection/StackObjectPool.cs

@@ -7,7 +7,7 @@ public sealed class StackObjectPool<T> : TrimmableCollectionObjectPoolBase<T, St
 		where T : class
 	{
 
-		public StackObjectPool(Func<T> factory, Action<T> recycler, Action<T> disposer, int capacity = DEFAULT_CAPACITY)
+		public StackObjectPool(Func<T> factory, Action<T>? recycler, Action<T>? disposer, int capacity = DEFAULT_CAPACITY)
 			: base(
 				  new Stack<T>(Math.Min(DEFAULT_CAPACITY, capacity)) /* Very very slight speed improvment when capacity is set. */,
 				  factory, recycler, disposer, capacity, false)
@@ -34,7 +34,7 @@ protected override bool Receive(T item)
 			return false;
 		}
 
-		protected override T TryRelease()
+		protected override T? TryRelease()
 		{
 			var p = Pool;
 			if (p != null && p.Count != 0)

source/GlobalSuppressions.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Contracts;
 
 namespace Open.Disposable
 {
@@ -30,13 +31,17 @@ public interface IObjectPool<T> : IDisposable
 		/// </summary>
 		/// <param name="item">The item to return if available.  Will be null if none avaialable.</param>
 		/// <returns>True if an item is provided.</returns>
-		bool TryTake(out T item);
+#if NETSTANDARD2_1
+		bool TryTake([NotNullWhen(true)] out T? item);
+#else
+		bool TryTake(out T? item);
+#endif
 
 		/// <summary>
 		/// If the pool has an item currently avaialable, removes it from the pool and returns it.
 		/// </summary>
 		/// <returns>The item to return if available.  Will be null if none avaialable.</returns>
-		T TryTake();
+		T? TryTake();
 
 
 		/// <summary>
@@ -64,6 +69,9 @@ public static class ObjectPoolExtensions
 		public static void Give<T>(this IObjectPool<T> target, IEnumerable<T> items)
 			where T : class
 		{
+			if (target is null) throw new ArgumentNullException(nameof(target));
+			Contract.EndContractBlock();
+
 			if (items == null) return;
 			foreach (var i in items)
 				target.Give(i);
@@ -80,6 +88,9 @@ public static void Give<T>(this IObjectPool<T> target, IEnumerable<T> items)
 		public static void Give<T>(this IObjectPool<T> target, T item1, T item2, params T[] items)
 			where T : class
 		{
+			if (target is null) throw new ArgumentNullException(nameof(target));
+			Contract.EndContractBlock();
+
 			target.Give(item1);
 			target.Give(item2);
 			target.Give(items);