Added TaskExtras.Partition

src/TaskExtras.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Threading.Tasks;
 
 namespace RLC.TaskChaining;
@@ -187,6 +189,37 @@ private static Task<T> DoRetry<T>(
         ));
   }
 
+  /// <summary>
+  /// Partitions a collection of <see cref="Task{T}"/> into faulted and fulfilled lists.
+  /// </summary>
+  /// <typeparam name="T">The underlying type of the tasks in <paramref name="tasks"/>.</typeparam>
+  /// <param name="tasks">The collection of tasks to partition.</param>
+  /// <returns>A tuple of the partitioned tasks.</returns>
+  public static Task<(IEnumerable<Task<T>> Faulted, IEnumerable<Task<T>> Fulfilled)> Partition<T>(
+    IEnumerable<Task<T>> tasks
+  )
+  {
+    return tasks.Aggregate<Task<T>, Task<(IEnumerable<Task<T>> Faulted, IEnumerable<Task<T>> Fulfilled)>>(
+      Task.FromResult(((IEnumerable<Task<T>>)new List<Task<T>>(), (IEnumerable<Task<T>>)new List<Task<T>>())),
+      ZipTasksWith<T, (IEnumerable<Task<T>> Faulted, IEnumerable<Task<T>> Fulfilled), (IEnumerable<Task<T>> Faulted, IEnumerable<Task<T>> Fulfilled), Exception>
+      (
+        (values, v) => (values.Faulted, values.Fulfilled.Append(Task.FromResult(v)).ToList()),
+        (values, v) => (values.Faulted.Append<Task<T>>(Task.FromException<T>(v)).ToList(), values.Fulfilled)
+      )
+    );
+  }
+
+  private static Func<Task<TAccum>, Task<TValue>, Task<TResult>> ZipTasksWith<TValue, TAccum, TResult, TException>(
+    Func<TAccum, TValue, TResult> f,
+    Func<TAccum, TException, TResult> g
+  ) where TException : Exception
+  {
+    return (b, a) => a.Then(
+      valueA => b.Then(valueB => f(valueB, valueA)),
+      error => b.Then(valueB => g(valueB, (TException)error))
+    );
+  }
+
 	/// <summary>
 	/// A function that performs retries of the <paramref name="supplier"/> if it fails.
 	/// </summary>

tests/unit/TaskExtrasPartitionTests.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+using RLC.TaskChaining;
+using Xunit;
+
+namespace RLC.TaskChainingTests;
+
+public class PartitionTests
+{
+  [Fact]
+  public async Task ItShouldPartition()
+  {
+    int expectedFulfills = 4;
+    int expectedFaults = 1;
+    List<Task<string>> tasks = new()
+    {
+      Task.FromResult("abc"),
+      Task.FromResult("def"),
+      Task.FromException<string>(new InvalidOperationException()),
+      Task.FromResult("ghi"),
+      TaskExtras.Defer(() => Task.FromResult("jkl"), TimeSpan.FromSeconds(1))
+    };
+
+    (IEnumerable<Task<string>> Faulted, IEnumerable<Task<string>> Fulfilled) partition = await TaskExtras.Partition(tasks);
+
+    Assert.Equal(expectedFaults, partition.Faulted.Count());
+    Assert.Equal(expectedFulfills, partition.Fulfilled.Count());
+  }
+}