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Provides object pools, function memoization, and caching utilities.


A value-type implementation of System.Tuple<...> with support for IStructuralEquatable and IStructuralComparable. The types are immutable.

var t = new Tuplet<int, bool, double>(1, true, 3.14);

Note: These types predate the introduction of System.ValueType<...> in .NET, which can provide a useful alternative.


Provides a set of methods to work with WeakReference<T> objects. For example, supports creating WeakReference<T> objects that contain a null reference, and adds a GetOrSetTarget method uses a function to get or set the target in a way similar to Lazy<T>.

WeakReference<string> w = WeakReferenceExtensions.Create<string>(null);

string s1 = w.GetTarget();
Console.WriteLine(s1 == null);

string s2 = w.GetOrSetTarget(() => DateTime.Now.ToString());

Object Pools


Provides a base class for object pools. It provides two symmetric methods:

  • T Allocate() to allocate an object from the pool.
  • void Free(T) to return an object to the pool.

To make freeing objects easier, it also provides a New method which returns a PooledObject<T> implementing IDisposable, so a using statement can be used to allocate and free an object.

When objects get returned to a pool, and they implement an IClearable interface, a call to Clear is made to restore the object to a state for future reuse.


Provides an implementation of an object pool using a Func<T> factory method to construct new instances of pooled objects. A pool also has a size of the number of objects to keep in the pool.

var pool = new ObjectPool<MyObject>(() => new MyObject(), size: 64);

MyObject obj1 = pool.Allocate();

using (PooledObject<MyObject> obj2 = pool.New())

PooledXYZ types

Specialized object pool implementations are provided for various .NET types:

  • PooledMemoryStream
  • PooledStringBuilder
  • PooledDictionary<TKey, TValue>
  • PooledHashSet<T>
  • PooledLinkedList<T>
  • PooledList<T>
  • PooledQueue<T>
  • PooledStackT>

For each such type PooledXYZ, a number of related types are provided:

  • PooledXYZ is the pooled equivalent of XYZ.
  • XYZPool is a pool for instances of PooledXYZ.
  • PooledXYZHolder is returned from New on the pool.

For example:

// Create a pool for 64 List<int> instances, passing a capacity of 1024 to the List<int> constructor.
var pool = ListPool<int>.Create(size: 64, capacity: 1024);

// Get a list from the pool. PooledList<T> inherits from List<T>.
PooledList<int> xs = pool.Allocate();

// Return the list to the pool; it will get cleared. Don't use xs anymore.

// Use disposable helper.
using (PooledListHolder<T> holder = pool.New())
    List<int> xs = holder.List;

Function Memoization

Memoization is a technique to transform a pure function into a compatible function which caches the result of evaluating the original function in order to speed up repeated invocations. Two forms of memoization are supported:

  • Regular memoization, where a Func<T, R> (or a function of a higher arity) has a cache that maps values of type T to type R, with the risk of keeping instances of T rooted.
  • Weak memoization, which only works for delegates where all arguments are constrained as class. The underlying cache uses weak references to avoid keepng instances of T rooted.

In order to use memoization, one first creates a memoizer using factory methods on Memoizer. These factory methods accept a cache factory and return an instance of type IMemoizer or IWeakMemoizer. Memoization cache factories are used to specify the policy for caching of function results. For example:

IMemoizationCacheFactory factory = MemoizationCacheFactory.CreateLru(16);
IMemoizer memoizer = Memoizer.Create(factory);

In this example, we use a least recently used (LRU) eviction strategy for the memoization caches that get created when memoizing functions. Other policies can be specified as well, including:

  • Unbounded for an unbounded cache.
  • Nop for no cache (useful for testing).
  • CreateEvictedByLowest and CreateEvictedByHighest, specifying a metric to rank entries by:
    • CreationTime - can be used to evict based on the initial invocation;
    • InvokeDuration - how long it took to invoke the function (e.g. to cache the expensive ones);
    • AverageAccessTime - how long it takes to locate the item in the cache (e.g. due to IEqualityComparer<T> costs);
    • HitCount - how often an entry is retrieved;
    • LastAccessTime - can be used to mimic LRU;
    • SpeedupFactor - a ratio of invocation time versus lookup time (e.g. to only keep entries that have a good speedup).

Once a memoizer instance is obtained, one can memoize functions using the Memoize method and various extension methods for higher arity functions. For example:

IMemoizedDelegate<Func<string, string>> toUpper = memoizer.Memoize(s => s.ToUpper());

Additional parameters can be specified to control caching behavior (e.g. whether or not to cache exceptions as well) and to specify an IEqualityComparer<T> used for key comparisons.

The resulting IMemoizedDelegate<TDelegate> provides access to:

  • the cache through a Cache property that can be used to inspect the cache, to clear it, etc.;
  • the memoized delegate through a Delegate property.

In order to invoke the memoized function, simply use the Delegate returned through the IMemoizedDelegate<TDelegate>. For example:

string foo = toUpper.Delegate("foo");

Subsequent invocations with the same argument(s) are subject to cache lookups.