[erlang-questions] Erlang 21, Stability and the murder of an innocent Statemachine

[Ingela Andin]

Hi!

2018-05-04 14:40 GMT+02:00 Mahesh Paolini-Subramanya <
mahesh@REDACTED>:

> To echo Heinz's point, is there a *reason* for the deprecation?
>
> Enquiring minds want to know...
>
>
>

Th point is to phase out gen_fsm. The deprecated warning is important to
get new users to choose gen_statem. Also if you have a living product you
will probably be better of in the long run changing to gen_statem. This
is not a complicated change and an exampel of how to do it is given in the
gen_fsm manual page. Of course we give lots of time to adopt. We have no
plan of removing the gen_fsm code swiftly, it is there in 20 and 21.
I can see the deprecating process needs to enhanchend, and yes it sort of
has more that one purpose which seems to conflict a bit.


Regards Ingela Erlang/OTP team


>
> On Fri, May 4, 2018 at 8:29 AM, Oliver Korpilla <oliver.korpilla@REDACTED>
> wrote:
>
>> Ah yes, dependencies! I see your problem now.
>>
>> We're using gen_statem for a test framework written in elixir for
>> telecoms. The FSM has been the least of our problems.
>>
>> I'm always amazed at the range of Erlang versions still in use. I keep
>> forgetting that.
>>
>> Oliver
>>
>>
>> On May 4, 2018 8:25:35 AM EDT, "Heinz N. Gies" <heinz@REDACTED>
>> wrote:
>>>
>>> Hi Oliver,
>>> I am not advocating to forbid migrating code to gen_statem when the
>>> maintainer feels it is an improvement for their code. I’m advocating for
>>> not forcing maintainers doing so for no reason.
>>>
>>> Karolis brought up another very good point I didn’t even think about.
>>> Code written with gen_statem will not be able to run on older erlang
>>> releases. While that’s probably not a issue on your own code where you
>>> control the releases completely it’s a nightmare for open source and
>>> libraries.
>>>
>>>
>>> On 4. May 2018, at 14:12, Oliver Korpilla <Oliver.Korpilla@REDACTED>
>>> wrote:
>>>
>>> Except for the init bug in 19.0 (which our infrastructure was fixed on
>>> for a long time) we found migrating to gen_statem a painless experience
>>> with decent improvements. But maybe we simply use a different or limited
>>> feature set?
>>>
>>> Oliver
>>>
>>> On May 4, 2018 8:03:11 AM EDT, "Heinz N. Gies" <heinz@REDACTED>
>>> wrote:
>>>>
>>>> I have thought of that but I don’t think that’s a real option.
>>>> Deprication warnings are important, this would turn all of them off which
>>>> doesn’t help code quality. I want to know if something is deprecated and
>>>> fix it in most cases. But as Karolis pointed out, it’s easy for a function
>>>> or two but for a whole behaviour it’s nearly impossible.
>>>>
>>>> It basically creates two erlang worlds, pre-statem and post-statem.
>>>>
>>>> The stack trace is not great but it’s not as bad, it’s somewhat
>>>> possible to just wrap the whole function calling it into a ifdef and call
>>>> it a day. Not great it still is a decent amount of code duplication but
>>>> it’s possible. https://github.com/Kyorai/clique/commit/b0e89de3cb
>>>> b56396b59a1023903c7259ec2ef145#diff-7a19efbe2afedfb64aa7ec6690e9a13e would
>>>> be an example. It’s more annoying then other changes but not nearly as bad
>>>> as the gen_fsm
>>>>
>>>> On 4. May 2018, at 13:58, Roger Lipscombe <roger@REDACTED>
>>>> wrote:
>>>>
>>>> On 4 May 2018 at 12:07, Karolis Petrauskas <k.petrauskas@REDACTED>
>>>> wrote:
>>>>
>>>>> I agree with Heinz. The deprecation of gen_fsm forced me to stuck on
>>>>> OTP 19 and I dont see any reasonable path to upgrade.
>>>>>
>>>>
>>>> We upgraded successfully to OTP 20 (and compiled against OTP 21) by
>>>> simply adding the following to the top of our gen_fsm modules:
>>>>
>>>> -compile([nowarn_deprecated_function]).  % gen_fsm is deprecated; use
>>>> gen_statem
>>>>
>>>> It'll be a problem when gen_fsm is *removed*, but until then, we'll
>>>> stick with this.
>>>>
>>>>
>>>>
>>> --
>>> Sent from my Android device with K-9 Mail. Please excuse my brevity.
>>>
>>>
>>>
>> --
>> Sent from my Android device with K-9 Mail. Please excuse my brevity.
>>
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>
>
> --
>
> *Mahesh Paolini-Subramanya
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