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

[Heinz N. Gies]

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/b0e89de3cbb56396b59a1023903c7259ec2ef145#diff-7a19efbe2afedfb64aa7ec6690e9a13e <https://github.com/Kyorai/clique/commit/b0e89de3cbb56396b59a1023903c7259ec2ef145#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 <mailto:roger@REDACTED>> wrote:
>> 
>> On 4 May 2018 at 12:07, Karolis Petrauskas <k.petrauskas@REDACTED <mailto: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.

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