Create helper method for building collections

Author: tautropfli

Ix.NET/Source/System.Linq.Async/System/Linq/AsyncEnumerableHelpers.cs

@@ -113,6 +113,21 @@ internal static async Task<Set<T>> ToSet<T>(IAsyncEnumerable<T> source, IEqualit
             return set;
         }
 
+        internal static async ValueTask<TResult> ToCollection<TSource, TCollection, TResult>(
+            this IAsyncEnumerable<TSource> source,
+            TCollection collection,
+            Func<TCollection, TResult> resultSelector,
+            CancellationToken cancellationToken)
+            where TCollection : ICollection<TSource>
+        {
+            await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
+            {
+                collection.Add(item);
+            }
+
+            return resultSelector(collection);
+        }
+
         internal struct ArrayWithLength<T>
         {
             public T[] Array;

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToHashSet.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
+using static System.Linq.Async.System.Linq.FunctionalHelpers;
 
 namespace System.Linq
 {
@@ -37,19 +38,10 @@ public static ValueTask<HashSet<TSource>> ToHashSetAsync<TSource>(this IAsyncEnu
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
 
-            return Core(source, comparer, cancellationToken);
-
-            static async ValueTask<HashSet<TSource>> Core(IAsyncEnumerable<TSource> source, IEqualityComparer<TSource>? comparer, CancellationToken cancellationToken)
-            {
-                var set = new HashSet<TSource>(comparer);
-
-                await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
-                {
-                    set.Add(item);
-                }
-
-                return set;
-            }
+            return source.ToCollection(
+                new HashSet<TSource>(comparer),
+                Identity,
+                cancellationToken);
         }
     }
 }

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToImmutableHashSet.cs

@@ -38,19 +38,10 @@ public static ValueTask<ImmutableHashSet<TSource>> ToImmutableHashSetAsync<TSour
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
 
-            return Core(source, equalityComparer, cancellationToken);
-
-            static async ValueTask<ImmutableHashSet<TSource>> Core(IAsyncEnumerable<TSource> source, IEqualityComparer<TSource>? equalityComparer, CancellationToken cancellationToken)
-            {
-                var builder = ImmutableHashSet.CreateBuilder(equalityComparer);
-
-                await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
-                {
-                    builder.Add(item);
-                }
-
-                return builder.ToImmutable();
-            }
+            return source.ToCollection(
+                ImmutableHashSet.CreateBuilder(equalityComparer),
+                static builder => builder.ToImmutable(),
+                cancellationToken);
         }
     }
 }

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToImmutableList.cs

@@ -25,19 +25,10 @@ public static ValueTask<ImmutableList<TSource>> ToImmutableListAsync<TSource>(th
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
 
-            return Core(source, cancellationToken);
-
-            static async ValueTask<ImmutableList<TSource>> Core(IAsyncEnumerable<TSource> source, CancellationToken cancellationToken = default)
-            {
-                var builder = ImmutableList.CreateBuilder<TSource>();
-
-                await foreach (var item in source.WithCancellation(cancellationToken))
-                {
-                    builder.Add(item);
-                }
-
-                return builder.ToImmutable();
-            }
+            return source.ToCollection(
+                ImmutableList.CreateBuilder<TSource>(),
+                static builder => builder.ToImmutable(),
+                cancellationToken);
         }
     }
 }

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToImmutableSortedSet.cs

@@ -38,19 +38,10 @@ public static ValueTask<ImmutableSortedSet<TSource>> ToImmutableSortedSetAsync<T
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
 
-            return Core(source, comparer, cancellationToken);
-
-            static async ValueTask<ImmutableSortedSet<TSource>> Core(IAsyncEnumerable<TSource> source, IComparer<TSource>? comparer, CancellationToken cancellationToken)
-            {
-                var builder = ImmutableSortedSet.CreateBuilder(comparer);
-
-                await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
-                {
-                    builder.Add(item);
-                }
-
-                return builder.ToImmutable();
-            }
+            return source.ToCollection(
+                ImmutableSortedSet.CreateBuilder(comparer),
+                static builder => builder.ToImmutable(),
+                cancellationToken);
         }
     }
 }

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToList.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
+using static System.Linq.Async.System.Linq.FunctionalHelpers;
 
 namespace System.Linq
 {
@@ -27,19 +28,7 @@ public static ValueTask<List<TSource>> ToListAsync<TSource>(this IAsyncEnumerabl
             if (source is IAsyncIListProvider<TSource> listProvider)
                 return listProvider.ToListAsync(cancellationToken);
 
-            return Core(source, cancellationToken);
-
-            static async ValueTask<List<TSource>> Core(IAsyncEnumerable<TSource> source, CancellationToken cancellationToken)
-            {
-                var list = new List<TSource>();
-
-                await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
-                {
-                    list.Add(item);
-                }
-
-                return list;
-            }
+            return source.ToCollection(new List<TSource>(), Identity, cancellationToken);
         }
     }
 }

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Utilities.cs

@@ -43,5 +43,20 @@ public static async ValueTask AddRangeAsync<T>(this List<T> list, IAsyncEnumerab
                 list.Add(item);
             }
         }
+
+        public static async ValueTask<TResult> ToCollection<TSource, TCollection, TResult>(
+            this IAsyncEnumerable<TSource> source,
+            TCollection collection,
+            Func<TCollection, TResult> resultSelector,
+            CancellationToken cancellationToken)
+            where TCollection : ICollection<TSource>
+        {
+            await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
+            {
+                collection.Add(item);
+            }
+
+            return resultSelector(collection);
+        }
     }
 }