reactive/Ix.NET/Source/System.Linq.Async/System/Threading/Tasks/AsyncEnumerableExtensions.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the Apache 2.0 License.
// See the LICENSE file in the project root for more information. 

using System.Collections.Generic;
using System.Runtime.CompilerServices;

namespace System.Threading.Tasks
{
    public static class AsyncEnumerableExtensions
    {
#if !BCL_HAS_CONFIGUREAWAIT // https://github.com/dotnet/coreclr/pull/21939

        /// <summary>Configures how awaits on the tasks returned from an async iteration will be performed.</summary>
        /// <typeparam name="T">The type of the objects being iterated.</typeparam>
        /// <param name="source">The source enumerable being iterated.</param>
        /// <param name="continueOnCapturedContext">Whether to capture and marshal back to the current context.</param>
        /// <returns>The configured enumerable.</returns>
        public static ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait<T>(
            this IAsyncEnumerable<T> source, bool continueOnCapturedContext) =>
            new ConfiguredCancelableAsyncEnumerable<T>(source, continueOnCapturedContext, cancellationToken: default);

        /// <summary>Sets the <see cref="CancellationToken"/> to be passed to <see cref="IAsyncEnumerable{T}.GetAsyncEnumerator(CancellationToken)"/> when iterating.</summary>
        /// <typeparam name="T">The type of the objects being iterated.</typeparam>
        /// <param name="source">The source enumerable being iterated.</param>
        /// <param name="cancellationToken">The <see cref="CancellationToken"/> to use.</param>
        /// <returns>The configured enumerable.</returns>
        public static ConfiguredCancelableAsyncEnumerable<T> WithCancellation<T>(
            this IAsyncEnumerable<T> source, CancellationToken cancellationToken) =>
            new ConfiguredCancelableAsyncEnumerable<T>(source, continueOnCapturedContext: true, cancellationToken);
#elif !REFERENCE_ASSEMBLY
        // we need to carry an impl that delegates to the BCL version of these

        /// <summary>Configures how awaits on the tasks returned from an async iteration will be performed.</summary>
        /// <typeparam name="T">The type of the objects being iterated.</typeparam>
        /// <param name="source">The source enumerable being iterated.</param>
        /// <param name="continueOnCapturedContext">Whether to capture and marshal back to the current context.</param>
        /// <returns>The configured enumerable.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait<T>(
            this IAsyncEnumerable<T> source, bool continueOnCapturedContext) => TaskExtensions.ConfigureAwait(source, continueOnCapturedContext);

        /// <summary>Sets the <see cref="CancellationToken"/> to be passed to <see cref="IAsyncEnumerable{T}.GetAsyncEnumerator(CancellationToken)"/> when iterating.</summary>
        /// <typeparam name="T">The type of the objects being iterated.</typeparam>
        /// <param name="source">The source enumerable being iterated.</param>
        /// <param name="cancellationToken">The <see cref="CancellationToken"/> to use.</param>
        /// <returns>The configured enumerable.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static ConfiguredCancelableAsyncEnumerable<T> WithCancellation<T>(
            this IAsyncEnumerable<T> source, CancellationToken cancellationToken) => TaskExtensions.WithCancellation(source, cancellationToken);

#else
        // Reference assembly, these won't be emmited, but keep these internal so we can compile
        /// <summary>Configures how awaits on the tasks returned from an async iteration will be performed.</summary>
        /// <typeparam name="T">The type of the objects being iterated.</typeparam>
        /// <param name="source">The source enumerable being iterated.</param>
        /// <param name="continueOnCapturedContext">Whether to capture and marshal back to the current context.</param>
        /// <returns>The configured enumerable.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait<T>(
            this IAsyncEnumerable<T> source, bool continueOnCapturedContext) => TaskExtensions.ConfigureAwait(source, continueOnCapturedContext);

        /// <summary>Sets the <see cref="CancellationToken"/> to be passed to <see cref="IAsyncEnumerable{T}.GetAsyncEnumerator(CancellationToken)"/> when iterating.</summary>
        /// <typeparam name="T">The type of the objects being iterated.</typeparam>
        /// <param name="source">The source enumerable being iterated.</param>
        /// <param name="cancellationToken">The <see cref="CancellationToken"/> to use.</param>
        /// <returns>The configured enumerable.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static ConfiguredCancelableAsyncEnumerable<T> WithCancellation<T>(
            this IAsyncEnumerable<T> source, CancellationToken cancellationToken) => TaskExtensions.WithCancellation(source, cancellationToken);
#endif

        public static ConfiguredCancelableAsyncEnumerable<T>.Enumerator GetConfiguredAsyncEnumerator<T>(this IAsyncEnumerable<T> enumerable, CancellationToken cancellationToken, bool continueOnCapturedContext)
        {
#if REFERENCE_ASSEMBLY
            return default;
#else
            return ConfigureAwait(enumerable, continueOnCapturedContext).WithCancellation(cancellationToken).GetAsyncEnumerator();
#endif
        }
    }
}