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

[Kenneth Lundin]

On Mon, May 7, 2018 at 8:54 AM, José Valim <jose.valim@REDACTED> wrote:

>
> What about documentation from the OTP team that outlines a deprecation
> policy? It may be a good opportunity to also outline other compatibility
> guarantees, such as the compiled bytecode guarantees and the node
> compatibility guarantees, if such are not yet documented.
>

I think it is a good idea to describe the OTP policy regarding deprecation,
backward compatibility, supported releases etc. in one place. Will try to
have it available before the OTP 21 release.

The Elixir policy with hard and soft deperecation is also interesting as we
need to make it
clearer what a depercation means.


But in short we use the deprecation mechanism to flag that a function och
application is no longer recommended for use in new code since there exist
another solution that we recomment to be used instead.

We don't remove deprecated functions or applications just like that and
some functions have to stay for a very long time (or forever) since there
is so much usage of them.

gen_fsm is an old module which is used a lot and it is not likely to
dissapear in a near future. I realize that the deprecated attribute inside
the module like this
-deprecated({start, 3, next_major_release}).
is somewhat misleading and we will try to improve this.

/Kenneth, Erlang/OTP


>
> We did define such document not long ago for Elixir. In terms of
> deprecations, we have two terms: "soft-deprecation" and "hard-deprecation".
> The soft-deprecation is added as soon as a new implementation exists. At
> this point we don't emit any warnings, but we do update the docs to say the
> feature will warn in the future and start to point folks towards better
> ways.
>
> A hard-deprecation is when we finally start emitting warnings. A
> hard-deprecation can only be added after an alternative exists for at least
> 2 Elixir releases. This is very important because it means that, once a
> feature is hard deprecated, you know you can use the proposed alternative
> and that alternative is supported at least two versions back.
>
> This is only necessary if a feature is being replaced. In case a feature
> is being removed, such as non-smp VM versions, you may skip directly to the
> "hard-deprecation" and emit warnings straight-away since there won’t be an
> alternative in the future anyway.
>
> I am not proposing for Erlang/OTP team to follow those rules and
> conventions but writing *some* rules as minimum guarantees may improve
> communication and help the community plan in terms of warnings,
> deprecations and removals accordingly. I would just avoid emitting
> deprecation warnings in the same version that an alternative is introduced,
> because it means library developers need to either only support the latest
> version or introduce conditionals (either at compile-time or runtime) to
> support multiple versions.
>
> *José Valimwww.plataformatec.com.br
> <http://www.plataformatec.com.br/>Founder and Director of R&D*
>
> --
>
>
> *José Valimwww.plataformatec.com.br
> <http://www.plataformatec.com.br/>Founder and Director of R&D*
>
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