ForEachAsyncExtensions.cs

using System.Threading;
using System.Threading.Tasks;

namespace System.Collections.Async
{
    /// <summary>
    /// Enables asynchronous 'foreach' enumeration over an IAsyncEnumerable
    /// </summary>
    public static class ForEachAsyncExtensions
    {
        /// <summary>
        /// Enumerates over all elements in the collection asynchronously
        /// </summary>
        /// <param name="enumerable">The collection of elements which can be enumerated asynchronously</param>
        /// <param name="action">A synchronous action to perform for every single item in the collection</param>
        /// <param name="cancellationToken">A cancellation token to stop enumerating</param>
        /// <returns>Returns a Task which does enumeration over elements in the collection</returns>
        public static async Task ForEachAsync(this IAsyncEnumerable enumerable, Action<object> action, CancellationToken cancellationToken = default(CancellationToken))
        {
            cancellationToken.ThrowIfCancellationRequested();

            using (var enumerator = await enumerable.GetAsyncEnumeratorAsync(cancellationToken)) {

                cancellationToken.ThrowIfCancellationRequested();

                while (await enumerator.MoveNextAsync(cancellationToken)) {

                    cancellationToken.ThrowIfCancellationRequested();

                    action(enumerator.Current);

                    cancellationToken.ThrowIfCancellationRequested();
                }
            }
        }

        /// <summary>
        /// Enumerates over all elements in the collection asynchronously
        /// </summary>
        /// <param name="enumerable">The collection of elements which can be enumerated asynchronously</param>
        /// <param name="action">An asynchronous action to perform for every single item in the collection</param>
        /// <param name="cancellationToken">A cancellation token to stop enumerating</param>
        /// <returns>Returns a Task which does enumeration over elements in the collection</returns>
        public static async Task ForEachAsync(this IAsyncEnumerable enumerable, Func<object, Task> action, CancellationToken cancellationToken = default(CancellationToken))
        {
            cancellationToken.ThrowIfCancellationRequested();

            using (var enumerator = await enumerable.GetAsyncEnumeratorAsync(cancellationToken)) {

                cancellationToken.ThrowIfCancellationRequested();

                while (await enumerator.MoveNextAsync(cancellationToken)) {

                    cancellationToken.ThrowIfCancellationRequested();

                    await action(enumerator.Current);

                    cancellationToken.ThrowIfCancellationRequested();
                }
            }
        }

        /// <summary>
        /// Enumerates over all elements in the collection asynchronously
        /// </summary>
        /// <typeparam name="T">The type of elements in the collection</typeparam>
        /// <param name="enumerable">The collection of elements which can be enumerated asynchronously</param>
        /// <param name="action">A synchronous action to perform for every single item in the collection</param>
        /// <param name="cancellationToken">A cancellation token to stop enumerating</param>
        /// <returns>Returns a Task which does enumeration over elements in the collection</returns>
        public static async Task ForEachAsync<T>(this IAsyncEnumerable<T> enumerable, Action<T> action, CancellationToken cancellationToken = default(CancellationToken))
        {
            cancellationToken.ThrowIfCancellationRequested();

            using (var enumerator = await enumerable.GetAsyncEnumeratorAsync(cancellationToken)) {

                cancellationToken.ThrowIfCancellationRequested();

                while (await enumerator.MoveNextAsync(cancellationToken)) {

                    cancellationToken.ThrowIfCancellationRequested();

                    action(enumerator.Current);

                    cancellationToken.ThrowIfCancellationRequested();
                }
            }
        }

        /// <summary>
        /// Enumerates over all elements in the collection asynchronously
        /// </summary>
        /// <typeparam name="T">The type of elements in the collection</typeparam>
        /// <param name="enumerable">The collection of elements which can be enumerated asynchronously</param>
        /// <param name="action">An asynchronous action to perform for every single item in the collection</param>
        /// <param name="cancellationToken">A cancellation token to stop enumerating</param>
        /// <returns>Returns a Task which does enumeration over elements in the collection</returns>
        public static async Task ForEachAsync<T>(this IAsyncEnumerable<T> enumerable, Func<T, Task> action, CancellationToken cancellationToken = default(CancellationToken))
        {
            cancellationToken.ThrowIfCancellationRequested();

            using (var enumerator = await enumerable.GetAsyncEnumeratorAsync(cancellationToken)) {

                cancellationToken.ThrowIfCancellationRequested();

                while (await enumerator.MoveNextAsync(cancellationToken)) {

                    cancellationToken.ThrowIfCancellationRequested();

                    await action(enumerator.Current);

                    cancellationToken.ThrowIfCancellationRequested();
                }
            }
        }
    }
}