Bug 18551 - CS0029 error when calling TaskFactory.ContinueWhenAll
Summary: CS0029 error when calling TaskFactory.ContinueWhenAll
Alias: None
Product: Compilers
Classification: Mono
Component: C# ()
Version: 2.10.x
Hardware: PC Linux
: --- normal
Target Milestone: ---
Assignee: Marek Safar
Depends on:
Reported: 2014-03-24 09:29 UTC by Andreas Spengler
Modified: 2014-05-02 11:55 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Andreas Spengler 2014-03-24 09:29:50 UTC
I am new to C#/.net development and am looking at some Extension methods from MSDN used in their Parallel Programming examples:

using System.Collections.Generic;

namespace System.Threading.Tasks
    public static partial class TaskFactoryExtensions

        // Works
        public static Task<Task[]> WhenAll(
            this TaskFactory factory, params Task[] tasks)
            return factory.ContinueWhenAll(tasks, completedTasks => completedTasks);

        // CS0029 error
        public static Task<Task<TAntecedentResult>[]> WhenAll<TAntecedentResult>(
            this TaskFactory factory, params Task<TAntecedentResult>[] tasks)
            return factory.ContinueWhenAll(tasks, completedTasks => completedTasks);

The first extension is ok, it is using the method

  public Task ContinueWhenAll (Task[] tasks, Action<Task[]> continuationAction)

from the System.Threading.Tasks.TaskFactory class.

The second extension however gives 

Error CS0029: Cannot implicitly convert type `System.Threading.Tasks.Task<System.Threading.Tasks.Task[]>' to `System.Threading.Tasks.Task<System.Threading.Tasks.Task<TAntecedentResult>[]>' (CS0029) (ParallelExtensionsExtras)

although there exists a method 

  public Task ContinueWhenAll<TAntecedentResult>(
             Task<TAntecedentResult>[] tasks, Action<Task<TAntecedentResult>[]> continuationAction)
Comment 1 Marek Safar 2014-05-02 11:55:34 UTC
Works fine with Mono 3.4.0 and most likely 3.2.x versions as well