C# extension methods for the TaskCompletionSource class.

//--------------------------------------------------------------------------
// 
//  Copyright (c) Microsoft Corporation.  All rights reserved. 
// 
//  File: TaskCompletionSourceExtensions.cs
//
//--------------------------------------------------------------------------

namespace System.Threading.Tasks
{
    /// <summary>Extension methods for TaskCompletionSource.</summary>
    public static class TaskCompletionSourceExtensions
    {
        /// <summary>Transfers the result of a Task to the TaskCompletionSource.</summary>
        /// <typeparam name="TResult">Specifies the type of the result.</typeparam>
        /// <param name="resultSetter">The TaskCompletionSource.</param>
        /// <param name="task">The task whose completion results should be transfered.</param>
        public static void SetFromTask<TResult>(this TaskCompletionSource<TResult> resultSetter, Task task)
        {
            switch (task.Status)
            {
                case TaskStatus.RanToCompletion:
                    resultSetter.SetResult(task is Task<TResult> ? ((Task<TResult>) task).Result : default(TResult));
                    break;
                case TaskStatus.Faulted:
                    resultSetter.SetException(task.Exception.InnerExceptions);
                    break;
                case TaskStatus.Canceled:
                    resultSetter.SetCanceled();
                    break;
                default: throw new InvalidOperationException("The task was not completed.");
            }
        }

        /// <summary>Transfers the result of a Task to the TaskCompletionSource.</summary>
        /// <typeparam name="TResult">Specifies the type of the result.</typeparam>
        /// <param name="resultSetter">The TaskCompletionSource.</param>
        /// <param name="task">The task whose completion results should be transfered.</param>
        public static void SetFromTask<TResult>(this TaskCompletionSource<TResult> resultSetter, Task<TResult> task)
        {
            SetFromTask(resultSetter, (Task) task);
        }

        /// <summary>Attempts to transfer the result of a Task to the TaskCompletionSource.</summary>
        /// <typeparam name="TResult">Specifies the type of the result.</typeparam>
        /// <param name="resultSetter">The TaskCompletionSource.</param>
        /// <param name="task">The task whose completion results should be transfered.</param>
        /// <returns>Whether the transfer could be completed.</returns>
        public static bool TrySetFromTask<TResult>(this TaskCompletionSource<TResult> resultSetter, Task task)
        {
            switch (task.Status)
            {
                case TaskStatus.RanToCompletion: return resultSetter.TrySetResult(task is Task<TResult> ? ((Task<TResult>) task).Result : default(TResult));
                case TaskStatus.Faulted: return resultSetter.TrySetException(task.Exception.InnerExceptions);
                case TaskStatus.Canceled: return resultSetter.TrySetCanceled();
                default: throw new InvalidOperationException("The task was not completed.");
            }
        }

        /// <summary>Attempts to transfer the result of a Task to the TaskCompletionSource.</summary>
        /// <typeparam name="TResult">Specifies the type of the result.</typeparam>
        /// <param name="resultSetter">The TaskCompletionSource.</param>
        /// <param name="task">The task whose completion results should be transfered.</param>
        /// <returns>Whether the transfer could be completed.</returns>
        public static bool TrySetFromTask<TResult>(this TaskCompletionSource<TResult> resultSetter, Task<TResult> task)
        {
            return TrySetFromTask(resultSetter, (Task) task);
        }
    }
}