It sounds good to me. A small but likely welcome change. A PR to further
explore this is welcome!
On Thu, Jul 1, 2021 at 12:26 AM Aaron Ross <superhawk...@gmail.com> wrote:
> +1
>
> I've encountered this in a similar context - I have one overall task that
> will spawn some number of data fetching tasks, but in some cases I know
> that the data fetch call will return no results so I stub the task with
> `Task.async(fn -> {:ok, []} end)`. The proposed `Task.completed/1` would be
> a great, more semantic replacement and has the benefit of not spawning an
> unneeded process.
>
> On Wednesday, June 30, 2021 at 3:22:07 PM UTC-7 Luke Bakken wrote:
>
>> ## Background
>>
>> I have an enumerable over which I fold and call Task.async based on the
>> data in the enumerable. I then Task.yield_many over the list of tasks, and
>> use Enum.zip to correlate the original enumerable with the results.
>>
>> I have a case where, during the fold I find that an entry is invalid for
>> running Task.async. It would be convenient to create an "already completed"
>> Task that contains an error result. For now, I'm still using Task.async to
>> basically return an :error tuple, which of course starts and links a
>> process.
>>
>> Of course, I could work around this by using maps, etc.
>>
>> I tried using %Task{} to create a "dummy" but calling Task.yield_many
>> with such an entry always blocks until the timeout.
>>
>> ## Proposal
>>
>> Add Task.completed/1 that creates an "already completed" Task that can
>> then be awaited / yielded to return the result used when completed/1 was
>> called:
>>
>> ```elixir
>> task = Task.completed({:error, :boom})
>> ```
>>
>> Awaiting or yielding on such a task returns the result immediately
>> without invoking a process.
>>
>> ## Other
>>
>> .NET has the following to achieve this behavior, for instance:
>>
>>
>> https://docs.microsoft.com/en-us/dotnet/api/system.threading.tasks.task.completedtask?view=net-5.0
>>
>>
>> https://docs.microsoft.com/en-us/dotnet/api/system.threading.tasks.task.fromresult?view=net-5.0
>>
>> Thanks for your consideration! If approved I would gladly implement this.
>> Luke
>>
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