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This library is based on classes from System.Collections.Generic that have been altered to take advantage of the new System.Span<T> and System.Buffers.ArrayPool<T> libraries to minimize memory allocations, improve performance, and/or allow greater interoperablity with modern API's.

Collections.Pooled supports both .NET Standard 2.0 (.NET Framework 4.6.1+) as well as an optimized build for .NET Core 2.1+. An extensive set of unit tests and benchmarks have been ported from corefx.

Total tests: 27501. Passed: 27501. Failed: 0. Skipped: 0.
Test Run Successful.
Test execution time: 9.9019 Seconds

Install-Package Collections.Pooled
dotnet add package Collections.Pooled
paket add Collections.Pooled

• .NET Core
• .NET Framework

PooledList<T> is based on the corefx source code for System.Collections.Generic.List<T>, modified to use ArrayPool for internal array-storage allocation, and to support Span<T>.

There are some API changes worth noting:

• Find and FindLast have become TryFind and TryFindLast, following the standard .NET "try" pattern.
• The new PooledList<T>.Span property returns a Span<T> over the portion of the internal array store that is populated. This span can be further sliced, or passed into other methods that can read from or write to a span.
  • Enumerating the Span property can be more than twice as fast as enumerating the list itself, but as we are unable to do the normal "collection modified during enumeration" checks, please use with caution.
  • The list is unable to increment its version-checking flag when setting values via the Span. Therefore, "collection modified during enumeration" checks can be bypassed. Please use with caution.
• GetRange now returns a Span<T>. For example, foo.GetRange(5, 100) is equivalent to foo.Span.Slice(5, 100).
• CopyTo now takes a Span<T> and doesn't offer any start-index or count parameters. Use the Span property and slicing instead.
• AddRange and InsertRange can now accept a ReadOnlySpan<T>.
• The new AddSpan and InsertSpan methods ensure the internal storage has the capacity to add the requested number of items, and return a Span<T> that can be used to write directly to that section of the internal storage. Caveats about "collection modified during enumeration" checks apply here as well.
• Delegate types such as Predicate<T> and Converter<T1, T2> have been replaced with standard Func<> equivalents.
• PooledList implements IDisposable. Disposing the list returns the internal array to the ArrayPool. If you forget to dispose the list, nothing will break, but memory allocations and GC pauses will be closer to those of List<T> (you will still benefit from pooling of intermediate arrays as the PooledList is resized).
• A selection of ToPooledList() extension methods are provided.
• You can optionally supply a custom implementation of ArrayPool<T> to the constructor, to be used instead of the default ArrayPool<T>.Shared pool.
• The clearMode constructor parameter gives you control over whether data is cleared before returning arrays to the ArrayPool.
• The sizeToCapacity constructor parameter causes the list to start out with Count == Capacity. All entries in the list will have the default value for the type, or if clearMode is set to ClearMode.Never then entries in the list may have a previously-used value from the array pool. This feature is primarily useful when working with value types and avoiding unnecessary allocations.

Adding items to a list is one area where ArrayPool helps us quite a bit:

PooledDictionary<TKey, TValue> is based on the corefx source code for System.Collections.Generic.Dictionary<TKey, TValue>, modified to use ArrayPool for internal storage allocation, and to support Span<T>.

There are some API changes worth noting:

• New methods include: AddRange, GetOrAdd, AddOrUpdate
• Both constructors and AddRange can take a sequence of KeyValuePair<TKey, TValue> objects, or a sequence of ValueTuple<TKey, TValue> objects.
• Significantly reduced memory allocations when adding many items.
• PooledDictionary implements IDisposable. Disposing the dictionary returns the internal arrays to the ArrayPool. If you forget to dispose the dictionary, nothing will break, but memory allocations and GC pauses will be closer to those of Dictionary<TKey, TValue> (you will still benefit from pooling of intermediate arrays as the PooledDictionary is resized).
• A selection of ToPooledDictionary() extension methods are provided.
• The ClearMode constructor parameter gives you control over whether data is cleared before returning arrays to the ArrayPool.

Adding to dictionaries is where using ArrayPool really has an impact:

PooledSet<T> is based on the corefx source code for System.Generic.Collections.HashSet<T>, modified to use ArrayPool for internal storage allocation, and to support ReadOnlySpan<T> for all set functions.

• Constructors, and all set methods have overloads that accept ReadOnlySpan<T>.
• There are also overloads that accept arrays but forward to the span implementation. They are present to avoid ambiguous method calls.
• PooledSet slightly outstrips HashSet in performance in almost every case, while allocating less memory. In cases where the internal arrays must be resized, PooledSet enjoys a substantial advantage.
• PooledSet implements IDisposable. Disposing the set returns the internal arrays to the ArrayPool. If you forget to dispose the set, nothing will break, but memory allocations and GC pauses will be closer to those of HashSet<T> (you will still benefit from pooling of intermediate arrays as the PooledSet is resized).
• A selection of ToPooledSet() extension methods are provided.
• The ClearMode constructor parameter gives you control over whether data is cleared before returning arrays to the ArrayPool.

Here's what pooling does for us when adding to a PooledSet.

PooledStack<T> is based on the corefx source code for System.Generic.Collections.Stack<T>, modified to use ArrayPool for internal storage allocation.

• Other than the ability to pass Spans into the constructor, the only other API change from Stack<T> is the addition of the RemoveWhere method: because sometimes you just need to remove something from a stack.
• Significantly reduced memory allocations when pushing many items.
• PooledStack implements IDisposable. Disposing the stack returns the internal array to the ArrayPool. If you forget to dispose the stack, nothing will break, but memory allocations and GC pauses will be closer to those of Stack<T> (you will still benefit from pooling of intermediate arrays as the PooledStack is resized).
• A selection of ToPooledStack() extension methods are provided.
• You can optionally supply a custom implementation of ArrayPool<T> to the constructor, to be used instead of the default ArrayPool<T>.Shared pool.
• The ClearMode constructor parameter gives you control over whether data is cleared before returning arrays to the ArrayPool.

Once again, pushing to a stack shows off some of the advantages of using ArrayPool:

PooledQueue<T> is based on the corefx source code for System.Generic.Collections.Queue<T>, modified to use ArrayPool for internal storage allocation.

• Other than the ability to pass Spans into the constructor, the only other API change from Queue<T> is the addition of the RemoveWhere method: because sometimes you just need to remove something from a queue.
• Significantly reduced memory allocations when enqueueing many items.
• PooledQueue implements IDisposable. Disposing the queue returns the internal array to the ArrayPool. If you forget to dispose the queue, nothing will break, but memory allocations and GC pauses will be closer to those of Queue<T> (you will still benefit from pooling of intermediate arrays as the PooledQueue is resized).
• A selection of ToPooledQueue() extension methods are provided.
• You can optionally supply a custom implementation of ArrayPool<T> to the constructor, to be used instead of the default ArrayPool<T>.Shared pool.
• The ClearMode constructor parameter gives you control over whether data is cleared before returning arrays to the ArrayPool.