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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Collections.Generic;
using System.Runtime.CompilerServices;
namespace System.Threading.Tasks
{
/// <summary>Provides a set of static methods for working with specific kinds of <see cref="Task"/> instances.</summary>
public static class TaskExtensions
{
/// <summary>Creates a proxy <see cref="Task"/> that represents the asynchronous operation of a <see cref="Task{Task}"/>.</summary>
/// <param name="task">The <see cref="Task{Task}"/> to unwrap.</param>
/// <returns>A <see cref="Task"/> that represents the asynchronous operation of the provided <see cref="Task{Task}"/>.</returns>
public static Task Unwrap(this Task<Task> task)
{
if (task == null)
{
throw new ArgumentNullException(nameof(task));
}
// If the task hasn't completed or was faulted/canceled, wrap it in an unwrap promise. Otherwise,
// it completed successfully. Return its inner task to avoid unnecessary wrapping, or if the inner
// task is null, return a canceled task to match the same semantics as CreateUnwrapPromise.
return
!task.IsCompletedSuccessfully ? Task.CreateUnwrapPromise<VoidTaskResult>(task, lookForOce: false) :
task.Result ??
Task.FromCanceled(new CancellationToken(true));
}
/// <summary>Creates a proxy <see cref="Task{TResult}"/> that represents the asynchronous operation of a wrapped <see cref="Task{TResult}"/>.</summary>
/// <param name="task">The wrapped <see cref="Task{TResult}"/> to unwrap.</param>
/// <returns>A <see cref="Task{TResult}"/> that represents the asynchronous operation of the provided wrapped <see cref="Task{TResult}"/>.</returns>
public static Task<TResult> Unwrap<TResult>(this Task<Task<TResult>> task)
{
if (task == null)
{
throw new ArgumentNullException(nameof(task));
}
// If the task hasn't completed or was faulted/canceled, wrap it in an unwrap promise. Otherwise,
// it completed successfully. Return its inner task to avoid unnecessary wrapping, or if the inner
// task is null, return a canceled task to match the same semantics as CreateUnwrapPromise.
return
!task.IsCompletedSuccessfully ? Task.CreateUnwrapPromise<TResult>(task, lookForOce: false) :
task.Result ??
Task.FromCanceled<TResult>(new CancellationToken(true));
}
/// <summary>Configures how awaits on the tasks returned from an async disposable will be performed.</summary>
/// <param name="source">The source async disposable.</param>
/// <param name="continueOnCapturedContext">Whether to capture and marshal back to the current context.</param>
/// <returns>The configured async disposable.</returns>
public static ConfiguredAsyncDisposable ConfigureAwait(this IAsyncDisposable source, bool continueOnCapturedContext) =>
new ConfiguredAsyncDisposable(source, continueOnCapturedContext);
/// <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);
}
}
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