Added LazyListUnsafe. Improved CopyTo methods for use with Span<T>. Migrated tests.

Author: electricessence

Open.Collections.sln

@@ -0,0 +1,31 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.31410.357
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Open.Collections", "source\Open.Collections.csproj", "{F1C64CD8-E90A-46C8-9373-3BAB5498CC14}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Open.Collections.Tests", "testing\Open.Collections.Tests\Open.Collections.Tests.csproj", "{44063AEE-8909-4A26-80BE-8623F5EBBA1F}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{F1C64CD8-E90A-46C8-9373-3BAB5498CC14}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F1C64CD8-E90A-46C8-9373-3BAB5498CC14}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F1C64CD8-E90A-46C8-9373-3BAB5498CC14}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F1C64CD8-E90A-46C8-9373-3BAB5498CC14}.Release|Any CPU.Build.0 = Release|Any CPU
+		{44063AEE-8909-4A26-80BE-8623F5EBBA1F}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{44063AEE-8909-4A26-80BE-8623F5EBBA1F}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{44063AEE-8909-4A26-80BE-8623F5EBBA1F}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{44063AEE-8909-4A26-80BE-8623F5EBBA1F}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {323AE57A-3C44-4EB8-890D-FD1107AADD8D}
+	EndGlobalSection
+EndGlobal

source/CollectionWrapper.cs

@@ -48,13 +48,9 @@ public virtual void Clear()
 		public virtual bool Remove(T item)
 			=> InternalSource.Remove(item);
 
-		/// <inheritdoc cref="ReadOnlyCollectionWrapper&lt;T, TCollection&gt;" />
+		/// <inheritdoc />
 		public override bool IsReadOnly
 			=> InternalSource.IsReadOnly;
-
-		/// <inheritdoc cref="ReadOnlyCollectionWrapper&lt;T, TCollection&gt;" />
-		public override void CopyTo(T[] array, int arrayIndex)
-			=> InternalSource.CopyTo(array, arrayIndex);
 		#endregion
 	}
 }

source/DictionaryToHashSetWrapper.cs

@@ -1,4 +1,5 @@
-using System.Collections;
+using System;
+using System.Collections;
 using System.Collections.Generic;
 
 namespace Open.Collections
@@ -13,12 +14,15 @@ public DictionaryToHashSetWrapper(IDictionary<T, bool> source)
 			InternalSource = source;
 		}
 
+		/// <inheritdoc />
 		public int Count
 			=> InternalSource.Count;
 
+		/// <inheritdoc />
 		public bool IsReadOnly
 			=> InternalSource.IsReadOnly;
 
+		/// <inheritdoc />
 		public virtual bool Add(T item)
 		{
 			if (InternalSource.ContainsKey(item))
@@ -35,31 +39,45 @@ public virtual bool Add(T item)
 			return true;
 		}
 
+		/// <inheritdoc />
 		public bool Remove(T item)
 			// ReSharper disable once AssignNullToNotNullAttribute
 			=> InternalSource.Remove(item);
 
+		/// <inheritdoc />
 		public void Clear()
 			=> InternalSource.Clear();
 
+		/// <inheritdoc />
 		public bool Contains(T item)
 			// ReSharper disable once AssignNullToNotNullAttribute
 			=> InternalSource.ContainsKey(item);
 
+		/// <inheritdoc />
 		public void CopyTo(T[] array, int arrayIndex)
 			=> InternalSource.Keys.CopyTo(array, arrayIndex);
 
+		/// <inheritdoc cref="ReadOnlyCollectionWrapper{T, TCollection}.CopyTo(Span{T})"/>
+		public virtual Span<T> CopyTo(Span<T> span)
+			=> InternalSource.Keys.CopyToSpan(span);
+
+		/// <summary>
+		/// Returns a copy of the underlying keys.
+		/// </summary>
 		public HashSet<T> ToHashSet()
 			=> new(InternalSource.Keys);
 
+		/// <inheritdoc />
 		public IEnumerator<T> GetEnumerator()
 			=> InternalSource.Keys.GetEnumerator();
 
+		/// <inheritdoc />
 		public void ExceptWith(IEnumerable<T> other)
 		{
 			foreach (var e in other) Remove(e);
 		}
 
+		/// <inheritdoc />
 		public void IntersectWith(IEnumerable<T> other)
 		{
 			foreach (var e in other)
@@ -69,24 +87,31 @@ public void IntersectWith(IEnumerable<T> other)
 			}
 		}
 
+		/// <inheritdoc />
 		public bool IsProperSubsetOf(IEnumerable<T> other)
 			=> ToHashSet().IsProperSubsetOf(other);
 
+		/// <inheritdoc />
 		public bool IsProperSupersetOf(IEnumerable<T> other)
 			=> ToHashSet().IsProperSupersetOf(other);
 
+		/// <inheritdoc />
 		public bool IsSubsetOf(IEnumerable<T> other)
 			=> ToHashSet().IsSubsetOf(other);
 
+		/// <inheritdoc />
 		public bool IsSupersetOf(IEnumerable<T> other)
 			=> ToHashSet().IsSupersetOf(other);
 
+		/// <inheritdoc />
 		public bool Overlaps(IEnumerable<T> other)
 			=> ToHashSet().Overlaps(other);
 
+		/// <inheritdoc />
 		public bool SetEquals(IEnumerable<T> other)
 			=> ToHashSet().SetEquals(other);
 
+		/// <inheritdoc />
 		public void SymmetricExceptWith(IEnumerable<T> other)
 		{
 			foreach (var e in other)
@@ -98,6 +123,7 @@ public void SymmetricExceptWith(IEnumerable<T> other)
 			}
 		}
 
+		/// <inheritdoc />
 		public void UnionWith(IEnumerable<T> other)
 		{
 			foreach (var e in other) Add(e);

source/Extensions.cs

@@ -816,9 +816,30 @@ public static IEnumerable<T> Weave<T>(this IEnumerable<IEnumerable<T>> source)
 			}
 		}
 
+		/// <summary>
+		/// Caches the results up to the last index requested.
+		/// </summary>
+		/// <param name="list">The source enumerable to cache.</param>
+		/// <param name="isEndless">When true, will throw an InvalidOperationException if anything causes the list to evaluate to completion.</param>
+		/// <returns>A LazyList<typeparamref name="T"/> for accessing the cached results.</returns>
 		public static LazyList<T> Memoize<T>(this IEnumerable<T> list, bool isEndless = false)
 			=> new(list, isEndless);
 
+		/// <summary>
+		/// Caches the results up to the last index requested.
+		/// 
+		/// WARNING:
+		/// - Is not thread safe.
+		/// - There is a risk of recursion.
+		/// - An endless enumerable may result in a stack overflow.
+		/// 
+		/// If any of the above are of concern, then use .Memoize() instead.
+		/// </summary>
+		/// <param name="list">The source enumerable to cache.</param>
+		/// <returns>A LazyList<typeparamref name="T"/> for accessing the cached results.</returns>
+		public static LazyListUnsafe<T> MemoizeUnsafe<T>(this IEnumerable<T> list)
+			=> new(list);
+
 		/// <summary>
 		/// .IndexOf extension optimized for an array.
 		/// </summary>
@@ -834,5 +855,29 @@ public static int IndexOf<T>(this T[] source, T value)
 			return -1;
 		}
 
+		/// <summary>
+		/// Copies the results to the provided span up to its length or until the end of the results.
+		/// </summary>
+		/// <param name="target">The span to copy to.</param>
+		/// <returns>
+		/// A span representing the results.
+		/// If the count was less than the target length, a new span representing the results.
+		/// Otherwise the target is returned.
+		/// </returns>
+		public static Span<T> CopyToSpan<T>(this IEnumerable<T> source, Span<T> target)
+		{
+			var len = target.Length;
+			if (len == 0) return target;
+
+			var count = 0;
+			foreach (var e in source)
+			{
+				target[count] = e;
+				if (len == ++count) return target;
+			}
+
+			return target.Slice(0, count);
+		}
+
 	}
 }

source/LazyList.cs

@@ -11,125 +11,46 @@
 
 namespace Open.Collections
 {
-	public class LazyList<T> : DisposableBase, IReadOnlyList<T>
+	/// <summary>
+	/// A a thread-safe list for caching the results of an enumerable.
+	/// Note: should be disposed manually whenever possible as the locking mechanism is a ReaderWriterLockSlim.
+	/// </summary>
+	public class LazyList<T> : LazyListUnsafe<T>
 	{
-		List<T> _cached;
-		IEnumerator<T> _enumerator;
-
 		ReaderWriterLockSlim Sync;
+		int _safeCount;
 
+		/// <summary>
+		/// A value indicating whether the results are known or expected to be finite.
+		/// A list that was constructed as endless but has reached the end of the results will return false.
+		/// </summary>
 		public bool IsEndless { get; private set; }
-		public LazyList(IEnumerable<T> source, bool isEndless = false)
+
+		public LazyList(IEnumerable<T> source, bool isEndless = false) : base(source)
 		{
-			_enumerator = source.GetEnumerator();
-			_cached = new List<T>();
 			Sync = new ReaderWriterLockSlim(LockRecursionPolicy.NoRecursion); // This is important as it's possible to recurse infinitely to generate a result. :(
 			IsEndless = isEndless; // To indicate if a source is not allowed to fully enumerate.
 		}
 
 		protected override void OnDispose()
 		{
-			using (Sync.WriteLock())
-			{
-				DisposeOf(ref _enumerator);
-				Nullify(ref _cached)?.Clear();
-			}
+			using (Sync.WriteLock()) base.OnDispose();
 
 			DisposeOf(ref Sync);
 		}
 
-		public T this[int index]
-		{
-			get
-			{
-				AssertIsAlive();
-
-				if (index < 0)
-					throw new ArgumentOutOfRangeException(nameof(index), "Cannot be less than zero.");
-				if (!EnsureIndex(index))
-					throw new ArgumentOutOfRangeException(nameof(index), "Greater than total count.");
-
-				return _cached[index];
-			}
-		}
+		private const string MARKED_ENDLESS = "This list is marked as endless and may never complete.";
 
-		private int _safeCount;
-		public int Count
+		/// <inheritdoc/>
+		public override int IndexOf(T item)
 		{
-			get
-			{
-				AssertIsAlive();
-				Finish();
-				return _cached.Count;
-			}
-		}
+			const string MESSAGE = MARKED_ENDLESS+" Use an enumerator, then Take(x).IndexOf().";
+			if (IsEndless) throw new InvalidOperationException(MESSAGE);
 
-		public bool TryGetValueAt(int index, out T value)
-		{
-			if (EnsureIndex(index))
-			{
-				value = _cached[index];
-				return true;
-			}
-
-			value = default!;
-			return false;
-		}
-
-		public IEnumerator<T> GetEnumerator()
-		{
-			AssertIsAlive();
-
-			var index = -1;
-			// Interlocked allows for multi-threaded access to this enumerator.
-			while (TryGetValueAt(Interlocked.Increment(ref index), out var value))
-				yield return value;
-		}
-
-		public int IndexOf(T item)
-		{
-			AssertIsAlive();
-			if (IsEndless)
-				throw new InvalidOperationException("This list is marked as endless and may never complete. Use an enumerator, then Take(x).IndexOf().");
-
-			var index = 0;
-			while (EnsureIndex(index))
-			{
-				var value = _cached[index];
-				if (value is null)
-				{
-					if (item is null) return index;
-				}
-				else if (value.Equals(item))
-					return index;
-
-				index++;
-			}
-
-			return -1;
-
-		}
-
-		public bool Contains(T item)
-		{
-			AssertIsAlive();
-			return IndexOf(item) != -1;
-		}
-
-		public void CopyTo(T[] array, int arrayIndex = 0)
-		{
-			AssertIsAlive();
-			var len = Math.Min(IsEndless ? int.MaxValue : Count, array.Length - arrayIndex);
-			for (var i = 0; i < len; i++)
-				array[i + arrayIndex] = this[i];
-		}
-
-		System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
-		{
-			return GetEnumerator();
+			return base.IndexOf(item);
 		}
 
-		private bool EnsureIndex(int maxIndex)
+		protected override bool EnsureIndex(int maxIndex)
 		{
 			if (maxIndex < _safeCount)
 				return true;
@@ -186,11 +107,11 @@ private bool EnsureIndex(int maxIndex)
 			return false;
 		}
 
-		private void Finish()
+		protected override void Finish()
 		{
 			if (IsEndless)
-				throw new InvalidOperationException("This list is marked as endless and may never complete.");
-			while (EnsureIndex(int.MaxValue)) { }
+				throw new InvalidOperationException(MARKED_ENDLESS);
+			base.Finish();
 		}
 
 	}