I put together a PR here: https://github.com/superhawk610/elixir/pull/1
I'd love to hear any feedback on the approach and implementation before
submitting to the official repo.
Thanks in advance!
On Thursday, July 1, 2021 at 12:33:57 AM UTC-7 José Valim wrote:
> 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 <superh...@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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