In my opinion we absolutely should not support this. It is an old
convention that was created to patch over problems with configuration in
releases, but it has been considered a bad pattern for quite some time now.
Not only are there better patterns available (see Phoenix and Ecto and
their init/1 callbacks as one example), but this is something that is being
addressed in the release tooling itself - currently with Distillery's
config provider framework, and perhaps some variation of that, or a better
alternative if one presents itself, when the tooling moves to core.
If you have dependencies which still use `{:system, "VAR"}`, you should
open issues to encourage maintainers to shift to the `init/1` callback
approach, or better, supporting configuration by parameter when possible.
The application env should be reserved for global config only.
Just my two cents,
Paul
On Mon, Aug 6, 2018 at 5:33 PM Ivan Yurov <ivan.your...@gmail.com> wrote:
> I agree that in general this is not something that should be defined in
> the language core or the standard lib.
> However, configuration (application env) is already managed by elixir, and
> this pattern to access system env var is a widely used by the libraries, so
> this might appear confusing for someone, that they set {:system, var} and
> it doesn't magically get resolved as it does with many libraries. :)
> Also, there's only one case when it really breaks, — when someone really
> wants to return {:system, something} on Application.get_env call, as you
> have pointed out. But why would they?
>
> Thanks, I'll take a closer look at Confex it seems to be doing exactly
> what I want. Even though there's a bit more of a boilerplate.
>
> On Monday, August 6, 2018 at 1:55:30 PM UTC-7, OvermindDL1 wrote:
>>
>> But what if I want to read it from a data store, or the database, or a
>> variety of other places.
>>
>> A whole configuration handling overhaul has been discussed on the forums
>> not long ago:
>>
>> https://elixirforum.com/t/proposal-moving-towards-discoverable-config-files/14302
>>
>> For now, https://hex.pm/packages/confex is a decent'ish shim that works
>> well enough for build-time configurations though. :-)
>>
>> But overall, things like that seem more suited for a configuration
>> library (that should be included in Elixir once it is sufficiently generic
>> enough and staged enough), though environment variables are common for the
>> configs, that doesn't mean that someone really doesn't just want `{:system,
>> var}` returned straight though, as can be the case..
>>
>> :-)
>>
>>
>> On Monday, August 6, 2018 at 1:15:08 PM UTC-6, Ivan Yurov wrote:
>>>
>>> While playing with deployment I found out that some libraries provide
>>> this feature that you can put {:system, var} in configuration and then it's
>>> resolved at runtime. However if it's in my code, I'd have to implement it
>>> on my own. Wouldn't it be nice if it was supported by Application module by
>>> default? Something like:
>>> def get_env(app, key, default \\ nil) do
>>> case :application.get_env(app, key, default) do
>>> {:system, var} ->
>>> System.get_env(var) || default
>>> rest ->
>>> rest
>>> end
>>> end
>>>
>>> Would it make sense?
>>>
>> --
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