Improve collection expressions usage (#626)

Source/SuperLinq.Async/Partition.cs

@@ -83,42 +83,4 @@ static async ValueTask<TResult> Core(
 			return resultSelector(lookup[true], lookup[false]);
 		}
 	}
-
-	private static async ValueTask<TResult> PartitionImpl<TKey, TElement, TResult>(
-		IAsyncEnumerable<IAsyncGrouping<TKey, TElement>> source,
-		int count, TKey? key1, TKey? key2, TKey? key3, IEqualityComparer<TKey>? comparer,
-		Func<IAsyncEnumerable<TElement>, IAsyncEnumerable<TElement>, IAsyncEnumerable<TElement>, IAsyncEnumerable<IAsyncGrouping<TKey, TElement>>, TResult> resultSelector,
-		CancellationToken cancellationToken)
-	{
-		comparer ??= EqualityComparer<TKey>.Default;
-
-		List<IAsyncGrouping<TKey, TElement>>? etc = null;
-
-		var groups = new[]
-		{
-			AsyncEnumerable.Empty<TElement>(),
-			AsyncEnumerable.Empty<TElement>(),
-			AsyncEnumerable.Empty<TElement>(),
-		};
-
-		await foreach (var e in source.WithCancellation(cancellationToken).ConfigureAwait(false))
-		{
-			var i = count > 0 && comparer.Equals(e.Key, key1) ? 0
-				  : count > 1 && comparer.Equals(e.Key, key2) ? 1
-				  : count > 2 && comparer.Equals(e.Key, key3) ? 2
-				  : -1;
-
-			if (i < 0)
-			{
-				etc ??= new List<IAsyncGrouping<TKey, TElement>>();
-				etc.Add(e);
-			}
-			else
-			{
-				groups[i] = e;
-			}
-		}
-
-		return resultSelector(groups[0], groups[1], groups[2], etc?.ToAsyncEnumerable() ?? AsyncEnumerable.Empty<IAsyncGrouping<TKey, TElement>>());
-	}
 }

Source/SuperLinq/Case.cs

@@ -42,7 +42,7 @@ public static IEnumerable<TResult> Case<TValue, TResult>(
 		IDictionary<TValue, IEnumerable<TResult>> sources)
 		where TValue : notnull
 	{
-		return Case(selector, sources, Enumerable.Empty<TResult>());
+		return Case(selector, sources, []);
 	}
 
 	/// <summary>

Source/SuperLinq/Collections/UpdatablePriorityQueue.cs

@@ -76,7 +76,7 @@ static UpdatablePriorityQueue()
 	/// </summary>
 	public UpdatablePriorityQueue()
 	{
-		_nodes = Array.Empty<(TElement, TPriority)>();
+		_nodes = [];
 		_priorityComparer = InitializeComparer(comparer: null);
 		_elementIndex = new(_elementComparer = EqualityComparer<TElement>.Default);
 	}
@@ -104,7 +104,7 @@ public UpdatablePriorityQueue(int initialCapacity)
 	/// </param>
 	public UpdatablePriorityQueue(IComparer<TPriority>? priorityComparer)
 	{
-		_nodes = Array.Empty<(TElement, TPriority)>();
+		_nodes = [];
 		_priorityComparer = InitializeComparer(priorityComparer);
 		_elementIndex = new(_elementComparer = EqualityComparer<TElement>.Default);
 	}
@@ -119,7 +119,7 @@ public UpdatablePriorityQueue(IComparer<TPriority>? priorityComparer)
 	/// </param>
 	public UpdatablePriorityQueue(IEqualityComparer<TElement>? elementComparer)
 	{
-		_nodes = Array.Empty<(TElement, TPriority)>();
+		_nodes = [];
 		_priorityComparer = InitializeComparer(comparer: null);
 		_elementComparer = elementComparer ?? EqualityComparer<TElement>.Default;
 		_elementIndex = new(_elementComparer);

Source/SuperLinq/FullGroupJoin.cs

@@ -225,7 +225,7 @@ IEnumerable<TResult> Core(IEqualityComparer<TKey> comparer)
 				if (alookup.Contains(b.Key))
 					continue;
 				// We can skip the lookup because we are iterating over keys not found in the first sequence
-				yield return resultSelector(b.Key, Enumerable.Empty<TFirst>(), b);
+				yield return resultSelector(b.Key, [], b);
 			}
 		}
 	}

Source/SuperLinq/If.cs

@@ -29,7 +29,7 @@ public static partial class SuperEnumerable
 	/// </remarks>
 	public static IEnumerable<TResult> If<TResult>(Func<bool> condition, IEnumerable<TResult> thenSource)
 	{
-		return If(condition, thenSource, Enumerable.Empty<TResult>());
+		return If(condition, thenSource, []);
 	}
 
 	/// <summary>

Source/SuperLinq/Partition.cs

@@ -74,41 +74,4 @@ public static TResult Partition<T, TResult>(
 		var lookup = source.ToLookup(predicate);
 		return resultSelector(lookup[true], lookup[false]);
 	}
-
-	private static TResult PartitionImpl<TKey, TElement, TResult>(
-		IEnumerable<IGrouping<TKey, TElement>> source,
-		int count, TKey? key1, TKey? key2, TKey? key3, IEqualityComparer<TKey>? comparer,
-		Func<IEnumerable<TElement>, IEnumerable<TElement>, IEnumerable<TElement>, IEnumerable<IGrouping<TKey, TElement>>, TResult> resultSelector)
-	{
-		comparer ??= EqualityComparer<TKey>.Default;
-
-		List<IGrouping<TKey, TElement>>? etc = null;
-
-		var groups = new[]
-		{
-			Enumerable.Empty<TElement>(),
-			Enumerable.Empty<TElement>(),
-			Enumerable.Empty<TElement>(),
-		};
-
-		foreach (var e in source)
-		{
-			var i = count > 0 && comparer.Equals(e.Key, key1) ? 0
-				  : count > 1 && comparer.Equals(e.Key, key2) ? 1
-				  : count > 2 && comparer.Equals(e.Key, key3) ? 2
-				  : -1;
-
-			if (i < 0)
-			{
-				etc ??= new List<IGrouping<TKey, TElement>>();
-				etc.Add(e);
-			}
-			else
-			{
-				groups[i] = e;
-			}
-		}
-
-		return resultSelector(groups[0], groups[1], groups[2], etc ?? Enumerable.Empty<IGrouping<TKey, TElement>>());
-	}
 }

Source/SuperLinq/Sequence.cs

@@ -91,7 +91,7 @@ public static IEnumerable<int> Sequence(int start, int stop, int step)
 			return Return(start);
 
 		if (Math.Sign((long)stop - start) != Math.Sign(step))
-			return Enumerable.Empty<int>();
+			return [];
 
 		return new SequenceIterator(start, step, (((long)stop - start) / step) + 1);
 	}

Source/SuperLinq/Take.cs

@@ -48,12 +48,13 @@ public static IEnumerable<TSource> Take<TSource>(IEnumerable<TSource> source, Ra
 		{
 			if (start.Value == 0 || (end.IsFromEnd && end.Value >= start.Value))
 			{
-				return Array.Empty<TSource>();
+				return [];
 			}
 		}
 		else if (!end.IsFromEnd)
 		{
-			return start.Value >= end.Value ? Array.Empty<TSource>()
+			return start.Value >= end.Value
+				? []
 				: TakeRangeIterator(source, start.Value, end.Value);
 		}
 

Source/SuperLinq/ToDataTable.cs

@@ -152,12 +152,12 @@ public static TTable ToDataTable<T, TTable>(this IEnumerable<T> source, TTable t
 		return table;
 	}
 
-	private static IEnumerable<MemberInfo> PrepareMemberInfos<T>(ICollection<Expression<Func<T, object>>> expressions)
+	private static IEnumerable<MemberInfo> PrepareMemberInfos<T>(Expression<Func<T, object>>[] expressions)
 	{
 		//
 		// If no lambda expressions supplied then reflect them off the source element type.
 		//
-		if (expressions.Count == 0)
+		if (expressions.Length == 0)
 		{
 			return typeof(T).GetMembers(BindingFlags.Public | BindingFlags.Instance)
 				.Where(m => m.MemberType == MemberTypes.Field

Tests/SuperLinq.Async.Test/AggregateByTest.cs

@@ -28,7 +28,7 @@ await ts.AggregateBy(keySelector, seedSelector, func, comparer)
 			seedSelector: x => 0,
 			func: (x, y) => x + y,
 			comparer: null,
-			expected: Enumerable.Empty<KeyValuePair<int, int>>());
+			expected: []);
 
 		yield return WrapArgs(
 			source: Enumerable.Range(0, 10),
@@ -134,7 +134,7 @@ await ts.AggregateBy(keySelector, seedSelector, func, comparer)
 			});
 
 		static object?[] WrapArgs<TSource, TKey, TAccumulate>(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, TAccumulate> seedSelector, Func<TAccumulate, TSource, TAccumulate> func, IEqualityComparer<TKey>? comparer, IEnumerable<KeyValuePair<TKey, TAccumulate>> expected)
-			=> new object?[] { source, keySelector, seedSelector, func, comparer, expected };
+			=> [source, keySelector, seedSelector, func, comparer, expected];
 	}
 
 	[Fact]
@@ -154,8 +154,8 @@ static IAsyncEnumerable<KeyValuePair<TKey, List<TSource>>> GroupBy<TSource, TKey
 				i => i % 2 == 0)
 			.ToDictionaryAsync(x => x.Key, x => x.Value);
 
-		Assert.True(oddsEvens[true].CollectionEqual(new[] { 2, 4, }));
-		Assert.True(oddsEvens[false].CollectionEqual(new[] { 1, 3, }));
+		Assert.True(oddsEvens[true].CollectionEqual([2, 4,]));
+		Assert.True(oddsEvens[false].CollectionEqual([1, 3,]));
 	}
 
 	[Fact]

Tests/SuperLinq.Async.Test/CopyToTest.cs

@@ -1,4 +1,5 @@
 using System.Collections.ObjectModel;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Test.Async;
 
@@ -9,10 +10,10 @@ public async Task NullArgumentTest()
 	{
 		_ = await Assert.ThrowsAsync<ArgumentNullException>(
 			"source",
-			async () => await default(IAsyncEnumerable<int>)!.CopyTo(Array.Empty<int>()));
+			async () => await default(IAsyncEnumerable<int>)!.CopyTo([]));
 		_ = await Assert.ThrowsAsync<ArgumentNullException>(
 			"source",
-			async () => await default(IAsyncEnumerable<int>)!.CopyTo(Array.Empty<int>(), 1));
+			async () => await default(IAsyncEnumerable<int>)!.CopyTo([], 1));
 		_ = await Assert.ThrowsAsync<ArgumentNullException>(
 			"list",
 			async () => await AsyncSeq<int>().CopyTo(default(int[])!));
@@ -26,10 +27,15 @@ public Task ThrowsOnNegativeIndex()
 	{
 		return Assert.ThrowsAsync<ArgumentOutOfRangeException>(
 			"index",
-			async () => await AsyncSeq<int>().CopyTo(Array.Empty<int>(), -1));
+			async () => await AsyncSeq<int>().CopyTo([], -1));
 	}
 
 	[Fact]
+	[SuppressMessage(
+		"Style",
+		"IDE0301:Simplify collection initialization",
+		Justification = "`[]` uses a list by default."
+	)]
 	public Task ThrowsOnTooMuchDataForArray()
 	{
 		return Assert.ThrowsAsync<IndexOutOfRangeException>(

Tests/SuperLinq.Async.Test/SplitTest.cs

@@ -22,7 +22,7 @@ public async Task SplitWithComparerUptoMaxCount()
 	{
 		await using var sequence = Enumerable.Range(1, 10).AsTestingSequence();
 		var result = sequence.Split(2, EqualityComparer.Create<int>((x, y) => x % 2 == y % 2), 2);
-		await result.AssertSequenceEqual(new[] { 1 }, new[] { 3 }, Enumerable.Range(5, 6));
+		await result.AssertSequenceEqual([1], [3], Enumerable.Range(5, 6));
 	}
 
 	[Fact]

Tests/SuperLinq.Test/AggregateByTest.cs

@@ -28,7 +28,7 @@ public static void AggregateBy_HasExpectedOutput<TSource, TKey, TAccumulate>(
 			seedSelector: x => 0,
 			func: (x, y) => x + y,
 			comparer: null,
-			expected: Enumerable.Empty<KeyValuePair<int, int>>());
+			expected: []);
 
 		yield return WrapArgs(
 			source: Enumerable.Range(0, 10),
@@ -134,7 +134,7 @@ public static void AggregateBy_HasExpectedOutput<TSource, TKey, TAccumulate>(
 			});
 
 		static object?[] WrapArgs<TSource, TKey, TAccumulate>(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, TAccumulate> seedSelector, Func<TAccumulate, TSource, TAccumulate> func, IEqualityComparer<TKey>? comparer, IEnumerable<KeyValuePair<TKey, TAccumulate>> expected)
-			=> new object?[] { source, keySelector, seedSelector, func, comparer, expected };
+			=> [source, keySelector, seedSelector, func, comparer, expected];
 	}
 
 	[Fact]

Tests/SuperLinq.Test/BacksertTest.cs

@@ -14,7 +14,7 @@ public void BacksertIsLazy()
 	public void BacksertWithNegativeIndex()
 	{
 		_ = Assert.Throws<ArgumentOutOfRangeException>(() =>
-			 new BreakingSequence<int>().Backsert(new[] { 97, 98, 99 }, -1));
+			 new BreakingSequence<int>().Backsert([97, 98, 99], -1));
 	}
 
 	[Theory]

Tests/SuperLinq.Test/BatchTest.cs

@@ -129,7 +129,7 @@ private static IEnumerable<IList<T>> GetBatches<T>(
 		};
 
 	public static IEnumerable<object[]> GetEmptySequences() =>
-		GetBatchTestSequences(Enumerable.Empty<int>());
+		GetBatchTestSequences([]);
 
 	[Theory]
 	[MemberData(nameof(GetEmptySequences))]

Tests/SuperLinq.Test/CopyToTest.cs

@@ -1,4 +1,5 @@
 using System.Collections.ObjectModel;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Test;
 
@@ -11,16 +12,16 @@ public void NullArgumentTest()
 	{
 		_ = Assert.Throws<ArgumentNullException>(
 			"source",
-			() => default(IEnumerable<int>)!.CopyTo(Array.Empty<int>()));
+			() => default(IEnumerable<int>)!.CopyTo((int[])[]));
 		_ = Assert.Throws<ArgumentNullException>(
 			"source",
 			() => default(IEnumerable<int>)!.CopyTo((IList<int>)[]));
 		_ = Assert.Throws<ArgumentNullException>(
 			"source",
-			() => default(IEnumerable<int>)!.CopyTo(Array.Empty<int>(), 1));
+			() => default(IEnumerable<int>)!.CopyTo([], 1));
 		_ = Assert.Throws<ArgumentNullException>(
 			"source",
-			() => default(IEnumerable<int>)!.CopyTo(Array.Empty<int>().AsSpan()));
+			() => default(IEnumerable<int>)!.CopyTo([]));
 		_ = Assert.Throws<ArgumentNullException>(
 			"array",
 			() => Seq<int>().CopyTo(default(int[])!));
@@ -37,7 +38,7 @@ public void ThrowsOnNegativeIndex()
 	{
 		_ = Assert.Throws<ArgumentOutOfRangeException>(
 			"index",
-			() => Seq<int>().CopyTo(Array.Empty<int>(), -1));
+			() => Seq<int>().CopyTo([], -1));
 	}
 
 	[Fact]
@@ -52,9 +53,13 @@ public void ThrowsOnTooMuchDataForArray()
 	}
 
 	[Fact]
+	[SuppressMessage(
+		"Style",
+		"IDE0301:Simplify collection initialization",
+		Justification = "`[]` uses a list by default."
+	)]
 	public void ThrowsOnTooMuchDataForIListArray()
 	{
-#pragma warning disable IDE0301 // Simplify collection initialization
 		_ = Assert.ThrowsAny<ArgumentException>(
 			() => Seq(1).CopyTo((IList<int>)Array.Empty<int>()));
 		_ = Assert.ThrowsAny<ArgumentException>(
@@ -63,7 +68,6 @@ public void ThrowsOnTooMuchDataForIListArray()
 			() => new List<int> { 1 }.AsEnumerable().CopyTo((IList<int>)Array.Empty<int>()));
 		_ = Assert.ThrowsAny<ArgumentException>(
 			() => new List<int> { 1 }.AsReadOnly().AsEnumerable().CopyTo((IList<int>)Array.Empty<int>()));
-#pragma warning restore IDE0301 // Simplify collection initialization
 	}
 
 	[Fact]

Tests/SuperLinq.Test/InsertTest.cs

@@ -12,7 +12,7 @@ public void InsertIsLazy()
 	public void InsertWithNegativeIndex()
 	{
 		_ = Assert.Throws<ArgumentOutOfRangeException>(() =>
-			 new BreakingSequence<int>().Insert(new[] { 97, 98, 99 }, -1));
+			 new BreakingSequence<int>().Insert([97, 98, 99], -1));
 	}
 
 	public static IEnumerable<object[]> GetSequences()

Tests/SuperLinq.Test/InterleaveTest.cs

@@ -77,7 +77,7 @@ public void TestInterleaveTwoEmptySequences()
 		using var sequenceB = TestingSequence.Of<int>();
 
 		var result = sequenceA.Interleave(sequenceB);
-		Assert.Equal(Enumerable.Empty<int>(), result);
+		Assert.Equal([], result);
 	}
 
 	/// <summary>

Tests/SuperLinq.Test/SplitTest.cs

@@ -22,7 +22,7 @@ public void SplitWithComparerUptoMaxCount()
 	{
 		using var sequence = Enumerable.Range(1, 10).AsTestingSequence();
 		var result = sequence.Split(2, EqualityComparer.Create<int>((x, y) => x % 2 == y % 2), 2).ToList();
-		result.AssertSequenceEqual(new[] { 1 }, new[] { 3 }, Enumerable.Range(5, 6));
+		result.AssertSequenceEqual([1], [3], Enumerable.Range(5, 6));
 	}
 
 	[Fact]