Removed closures in favour of private static methods to close issue #906

MoreLinq.Test/RankTest.cs

@@ -124,7 +124,7 @@ public void TestRankGroupedItems()
                 .Concat(Enumerable.Range(0, count))
                 .Concat(Enumerable.Range(0, count));
             using var ts = sequence.AsTestingSequence();
-            var result = ts.Rank();
+            var result = ts.Rank().ToArray();
 
             Assert.That(result.Distinct().Count(), Is.EqualTo(count));
             Assert.That(result, Is.EqualTo(sequence.Reverse().Select(x => x + 1)));

MoreLinq/Assert.cs

@@ -65,7 +65,9 @@ public static IEnumerable<TSource> Assert<TSource>(this IEnumerable<TSource> sou
             if (source == null) throw new ArgumentNullException(nameof(source));
             if (predicate == null) throw new ArgumentNullException(nameof(predicate));
 
-            return _(); IEnumerable<TSource> _()
+            return _(source, predicate, errorSelector);
+
+            static IEnumerable<TSource> _(IEnumerable<TSource> source, Func<TSource, bool> predicate, Func<TSource, Exception>? errorSelector)
             {
                 foreach (var element in source)
                 {

MoreLinq/AssertCount.cs

@@ -70,7 +70,9 @@ public static IEnumerable<TSource> AssertCount<TSource>(this IEnumerable<TSource
             if (count < 0) throw new ArgumentOutOfRangeException(nameof(count));
             if (errorSelector == null) throw new ArgumentNullException(nameof(errorSelector));
 
-            return _(); IEnumerable<TSource> _()
+            return _(source, count, errorSelector);
+
+            static IEnumerable<TSource> _(IEnumerable<TSource> source, int count, Func<int, int, Exception> errorSelector)
             {
                 if (source.TryAsCollectionLike() is { Count: var collectionCount }
                     && collectionCount.CompareTo(count) is var comparison && comparison != 0)

MoreLinq/Backsert.cs

@@ -65,10 +65,10 @@ public static IEnumerable<T> Backsert<T>(this IEnumerable<T> first, IEnumerable<
             {
                 < 0 => throw new ArgumentOutOfRangeException(nameof(index), "Index cannot be negative."),
                 0 => first.Concat(second),
-                _ => _()
+                _ => _(first, second, index)
             };
 
-            IEnumerable<T> _()
+            static IEnumerable<T> _(IEnumerable<T> first, IEnumerable<T> second, int index)
             {
                 using var e = first.CountDown(index, ValueTuple.Create).GetEnumerator();
 

MoreLinq/Batch.cs

@@ -86,7 +86,9 @@ public static IEnumerable<TResult> Batch<TSource, TResult>(this IEnumerable<TSou
             if (size <= 0) throw new ArgumentOutOfRangeException(nameof(size));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(source, size, resultSelector);
+
+            static IEnumerable<TResult> _(IEnumerable<TSource> source, int size, Func<TSource[], TResult> resultSelector)
             {
                 switch (source)
                 {

MoreLinq/Cartesian.g.cs

@@ -69,7 +69,12 @@
             if (second == null) throw new ArgumentNullException(nameof(second));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(first, second, resultSelector);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<T1> first,
+                IEnumerable<T2> second,
+                Func<T1, T2, TResult> resultSelector)
             {
                 IEnumerable<T2> secondMemo;
 
@@ -123,7 +128,13 @@
             if (third == null) throw new ArgumentNullException(nameof(third));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(first, second, third, resultSelector);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<T1> first,
+                IEnumerable<T2> second,
+                IEnumerable<T3> third,
+                Func<T1, T2, T3, TResult> resultSelector)
             {
                 IEnumerable<T2> secondMemo;
                 IEnumerable<T3> thirdMemo;
@@ -185,7 +196,14 @@
             if (fourth == null) throw new ArgumentNullException(nameof(fourth));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(first, second, third, fourth, resultSelector);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<T1> first,
+                IEnumerable<T2> second,
+                IEnumerable<T3> third,
+                IEnumerable<T4> fourth,
+                Func<T1, T2, T3, T4, TResult> resultSelector)
             {
                 IEnumerable<T2> secondMemo;
                 IEnumerable<T3> thirdMemo;
@@ -255,7 +273,15 @@
             if (fifth == null) throw new ArgumentNullException(nameof(fifth));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(first, second, third, fourth, fifth, resultSelector);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<T1> first,
+                IEnumerable<T2> second,
+                IEnumerable<T3> third,
+                IEnumerable<T4> fourth,
+                IEnumerable<T5> fifth,
+                Func<T1, T2, T3, T4, T5, TResult> resultSelector)
             {
                 IEnumerable<T2> secondMemo;
                 IEnumerable<T3> thirdMemo;
@@ -333,7 +359,16 @@
             if (sixth == null) throw new ArgumentNullException(nameof(sixth));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(first, second, third, fourth, fifth, sixth, resultSelector);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<T1> first,
+                IEnumerable<T2> second,
+                IEnumerable<T3> third,
+                IEnumerable<T4> fourth,
+                IEnumerable<T5> fifth,
+                IEnumerable<T6> sixth,
+                Func<T1, T2, T3, T4, T5, T6, TResult> resultSelector)
             {
                 IEnumerable<T2> secondMemo;
                 IEnumerable<T3> thirdMemo;
@@ -419,7 +454,17 @@
             if (seventh == null) throw new ArgumentNullException(nameof(seventh));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(first, second, third, fourth, fifth, sixth, seventh, resultSelector);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<T1> first,
+                IEnumerable<T2> second,
+                IEnumerable<T3> third,
+                IEnumerable<T4> fourth,
+                IEnumerable<T5> fifth,
+                IEnumerable<T6> sixth,
+                IEnumerable<T7> seventh,
+                Func<T1, T2, T3, T4, T5, T6, T7, TResult> resultSelector)
             {
                 IEnumerable<T2> secondMemo;
                 IEnumerable<T3> thirdMemo;
@@ -513,7 +558,18 @@
             if (eighth == null) throw new ArgumentNullException(nameof(eighth));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(first, second, third, fourth, fifth, sixth, seventh, eighth, resultSelector);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<T1> first,
+                IEnumerable<T2> second,
+                IEnumerable<T3> third,
+                IEnumerable<T4> fourth,
+                IEnumerable<T5> fifth,
+                IEnumerable<T6> sixth,
+                IEnumerable<T7> seventh,
+                IEnumerable<T8> eighth,
+                Func<T1, T2, T3, T4, T5, T6, T7, T8, TResult> resultSelector)
             {
                 IEnumerable<T2> secondMemo;
                 IEnumerable<T3> thirdMemo;

MoreLinq/Cartesian.g.tt

@@ -115,7 +115,14 @@ Func<<#= string.Join(", ", from x in o.Arguments select "T" + x.Number) #>, TRes
 <#      } #>
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(<#= string.Join(", ", from x in o.Arguments select x.Ordinal)  #>, resultSelector);
+
+            static IEnumerable<TResult> _(
+                <#      foreach (var arg in o.Arguments) { #>
+IEnumerable<T<#= arg.Number #>> <#= arg.Ordinal #>,
+                <#
+        } #>
+Func<<#= string.Join(", ", from x in o.Arguments select "T" + x.Number) #>, TResult> resultSelector)
             {
 <#      foreach (var arg in o.Arguments.Skip(1)) { #>
                 IEnumerable<T<#= arg.Number #>> <#= arg.Ordinal #>Memo;

MoreLinq/Choose.cs

@@ -55,7 +55,11 @@ public static IEnumerable<TResult> Choose<T, TResult>(this IEnumerable<T> source
             if (source == null) throw new ArgumentNullException(nameof(source));
             if (chooser == null) throw new ArgumentNullException(nameof(chooser));
 
-            return _(); IEnumerable<TResult> _()
+            return _(source, chooser);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<T> source,
+                Func<T, (bool, TResult)> chooser)
             {
                 foreach (var item in source)
                 {

MoreLinq/CountBy.cs

@@ -55,7 +55,9 @@ public static IEnumerable<KeyValuePair<TKey, int>> CountBy<TSource, TKey>(this I
             if (source == null) throw new ArgumentNullException(nameof(source));
             if (keySelector == null) throw new ArgumentNullException(nameof(keySelector));
 
-            return _(); IEnumerable<KeyValuePair<TKey, int>> _()
+            return _(source, keySelector, comparer);
+
+            static IEnumerable<KeyValuePair<TKey, int>> _(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? comparer)
             {
                 List<TKey> keys;
                 List<int> counts;

MoreLinq/CountDown.cs

@@ -58,12 +58,15 @@ public static IEnumerable<TResult> CountDown<T, TResult>(this IEnumerable<T> sou
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
             return source.TryAsListLike() is { } listLike
-                   ? IterateList(listLike)
+                   ? IterateList(listLike, count, resultSelector)
                    : source.TryAsCollectionLike() is { } collectionLike
-                     ? IterateCollection(collectionLike)
-                     : IterateSequence();
+                     ? IterateCollection(collectionLike, count, resultSelector)
+                     : IterateSequence(source, count, resultSelector);
 
-            IEnumerable<TResult> IterateList(ListLike<T> list)
+            static IEnumerable<TResult> IterateList(
+                ListLike<T> list,
+                int count,
+                Func<T, int?, TResult> resultSelector)
             {
                 var listCount = list.Count;
                 var countdown = Math.Min(count, listCount);
@@ -72,14 +75,20 @@ IEnumerable<TResult> IterateList(ListLike<T> list)
                     yield return resultSelector(list[i], listCount - i <= count ? --countdown : null);
             }
 
-            IEnumerable<TResult> IterateCollection(CollectionLike<T> collection)
+            static IEnumerable<TResult> IterateCollection(
+                CollectionLike<T> collection,
+                int count,
+                Func<T, int?, TResult> resultSelector)
             {
                 var i = collection.Count;
                 foreach (var item in collection)
                     yield return resultSelector(item, i-- <= count ? i : null);
             }
 
-            IEnumerable<TResult> IterateSequence()
+            static IEnumerable<TResult> IterateSequence(
+                IEnumerable<T> source,
+                int count,
+                Func<T, int?, TResult> resultSelector)
             {
                 var queue = new Queue<T>(Math.Max(1, count + 1));
 

MoreLinq/DistinctBy.cs

@@ -78,7 +78,12 @@ public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TS
             if (source == null) throw new ArgumentNullException(nameof(source));
             if (keySelector == null) throw new ArgumentNullException(nameof(keySelector));
 
-            return _(); IEnumerable<TSource> _()
+            return _(source, keySelector, comparer);
+
+            static IEnumerable<TSource> _(
+                IEnumerable<TSource> source,
+                Func<TSource, TKey> keySelector,
+                IEqualityComparer<TKey>? comparer)
             {
                 var knownKeys = new HashSet<TKey>(comparer);
                 foreach (var element in source)

MoreLinq/EndsWith.cs

@@ -78,14 +78,14 @@ public static bool EndsWith<T>(this IEnumerable<T> first, IEnumerable<T> second,
             return second.TryAsCollectionLike() is { Count: var secondCount }
                    ? first.TryAsCollectionLike() is { Count: var firstCount } && secondCount > firstCount
                      ? false
-                     : Impl(second, secondCount)
-                   : Impl(secondList = second.ToList(), secondList.Count);
+                     : Impl(first, second, secondCount, comparer)
+                   : Impl(first, secondList = second.ToList(), secondList.Count, comparer);
 #pragma warning restore IDE0075 // Simplify conditional expression
 
-            bool Impl(IEnumerable<T> snd, int count)
+            static bool Impl(IEnumerable<T> first, IEnumerable<T> second, int count, IEqualityComparer<T> comparer)
             {
                 using var firstIter = first.TakeLast(count).GetEnumerator();
-                return snd.All(item => firstIter.MoveNext() && comparer.Equals(firstIter.Current, item));
+                return second.All(item => firstIter.MoveNext() && comparer.Equals(firstIter.Current, item));
             }
         }
     }

MoreLinq/ExceptBy.cs

@@ -79,9 +79,13 @@ public static IEnumerable<TSource> ExceptBy<TSource, TKey>(this IEnumerable<TSou
             if (second == null) throw new ArgumentNullException(nameof(second));
             if (keySelector == null) throw new ArgumentNullException(nameof(keySelector));
 
-            return Impl();
+            return Impl(first, second, keySelector, keyComparer);
 
-            IEnumerable<TSource> Impl()
+            static IEnumerable<TSource> Impl(
+                IEnumerable<TSource> first,
+                IEnumerable<TSource> second,
+                Func<TSource, TKey> keySelector,
+                IEqualityComparer<TKey>? keyComparer)
             {
                 // TODO Use ToHashSet
                 var keys = new HashSet<TKey>(second.Select(keySelector), keyComparer);

MoreLinq/Exclude.cs

@@ -41,10 +41,10 @@ public static IEnumerable<T> Exclude<T>(this IEnumerable<T> sequence, int startI
             {
                 < 0 => throw new ArgumentOutOfRangeException(nameof(count)),
                 0 => sequence,
-                _ => _()
+                _ => _(sequence, startIndex, count)
             };
 
-            IEnumerable<T> _()
+            static IEnumerable<T> _(IEnumerable<T> sequence, int startIndex, int count)
             {
                 var index = 0;
                 var endIndex = startIndex + count;

MoreLinq/Experimental/Async/Merge.cs

@@ -85,9 +85,9 @@ public static IAsyncEnumerable<T> Merge<T>(this IEnumerable<IAsyncEnumerable<T>>
             if (sources is null) throw new ArgumentNullException(nameof(sources));
             if (maxConcurrent <= 0) throw new ArgumentOutOfRangeException(nameof(maxConcurrent));
 
-            return Async();
+            return Async(sources, maxConcurrent);
 
-            async IAsyncEnumerable<T> Async([EnumeratorCancellation]CancellationToken cancellationToken = default)
+            static async IAsyncEnumerable<T> Async(IEnumerable<IAsyncEnumerable<T>> sources, int maxConcurrent, [EnumeratorCancellation]CancellationToken cancellationToken = default)
             {
                 using var thisCancellationTokenSource = new CancellationTokenSource();
 

MoreLinq/Experimental/Await.cs

@@ -424,11 +424,20 @@ public static IAwaitQuery<TResult> AwaitCompletion<T, TTaskResult, TResult>(
 
             return
                 AwaitQuery.Create(
-                    options => Impl(options.MaxConcurrency,
+                    options => Impl(source,
+                                    evaluator,
+                                    resultSelector,
+                                    options.MaxConcurrency,
                                     options.Scheduler ?? TaskScheduler.Default,
                                     options.PreserveOrder));
 
-            IEnumerable<TResult> Impl(int? maxConcurrency, TaskScheduler scheduler, bool ordered)
+            static IEnumerable<TResult> Impl(
+                IEnumerable<T> source,
+                Func<T, CancellationToken, Task<TTaskResult>> evaluator,
+                Func<T, Task<TTaskResult>, TResult> resultSelector,
+                int? maxConcurrency,
+                TaskScheduler scheduler,
+                bool ordered)
             {
                 // A separate task will enumerate the source and launch tasks.
                 // It will post all progress as notices to the collection below.

MoreLinq/Experimental/Batch.cs

@@ -145,7 +145,12 @@ public static IEnumerable<TResult>
             if (bucketProjectionSelector == null) throw new ArgumentNullException(nameof(bucketProjectionSelector));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(source, size, pool, bucketProjectionSelector, resultSelector);
+
+            static IEnumerable<TResult> _(
+                IEnumerable<TSource> source, int size, ArrayPool<TSource> pool,
+                Func<ICurrentBuffer<TSource>, IEnumerable<TBucket>> bucketProjectionSelector,
+                Func<IEnumerable<TBucket>, TResult> resultSelector)
             {
                 using var batch = source.Batch(size, pool);
                 var bucket = bucketProjectionSelector(batch.CurrentBuffer);

MoreLinq/FallbackIfEmpty.cs

@@ -161,7 +161,16 @@ static IEnumerable<T> FallbackIfEmptyImpl<T>(IEnumerable<T> source,
             int? count, T? fallback1, T? fallback2, T? fallback3, T? fallback4,
             IEnumerable<T>? fallback)
         {
-            return _(); IEnumerable<T> _()
+            return _(source, count, fallback1, fallback2, fallback3, fallback4, fallback);
+
+            static IEnumerable<T> _(
+                IEnumerable<T> source,
+                int? count,
+                T? fallback1,
+                T? fallback2,
+                T? fallback3,
+                T? fallback4,
+                IEnumerable<T>? fallback)
             {
                 if (source.TryAsCollectionLike() is null or { Count: > 0 })
                 {