Alternative command line friendly syntax for string list

[patriknw]

We have the need to override string lists from command line -D parameters. That is not possible at the moment.
Example: akka.cluster.seed-nodes=["akka.tcp://TestApp@host1:2552", "akka.tcp://TestApp@host2:2552"]

That gives error: ConfigException$WrongType: system properties: akka.cluster.seed-nodes has type STRING rather than LIST

Some kind of alternative syntax would be nice.

As discussed the following syntax would be ok:
-Dakka.cluster.seed-nodes.0=akka.tcp://TestApp@host1:2552 -Dakka.cluster.seed-nodes.1=akka.tcp://TestApp@host2:2552

[slandelle]

Sorry to jump in.
Wouldn't it be better to support comma separated values?
-Dakka.cluster.seed-nodes=akka.tcp://TestApp@host1:2552,akka.tcp://TestApp@host2:2552

[havocp]

There are a few problems with having syntax within the string rather than having distinct strings:

• there are usually 2-3 layers of quoting (shell, properties file, the syntax)
• it's a syntax to document/learn/implement (how do you escape a comma?)
• you would get syntax errors rather than type errors when there's an actual type error, which could be confusing

We could also just support a JSON array syntax, but it would have a similar issue.

[slandelle]

OK, got it, thanks!

[havocp]

Thanks for the comment though, I am not sure we have the perfect solution here yet, this is just the idea we have so far.

[patriknw]

Hi @havocp, have you thought any more about this? Is it possible to complete the remaining things and release a new minor version?

[havocp]

I think the PR is ready, I could make a release on Monday.

[patriknw]

great, thanks
then we can use it for akka 2.2-RC1

[havocp]

1.0.1 should be available/working

[patriknw]

Thanks

[nilsga]

Is this somehow possible with environment variables as well?

[havocp]

The lib only uses env variables if they are explicitly pulled in by the .conf file as a ${} reference. The only way I know to do a list as env vars is something like:

 emails += ${?EMAIL_1}
 emails += ${?EMAIL_2}

[RichardBradley]

This feature doesn't appear to be documented anywhere except here and http://stackoverflow.com/questions/16202501/how-can-i-override-a-typesafe-config-list-value-on-the-command-line and https://github.com/typesafehub/config/blob/f6680a5dad51d992139d45a84fad734f1778bf50/NEWS.md#101-may-19-2013 -- have I missed something?

I think it would be nice to add something to the docs about this. I'll see if I have time to make a PR in the coming weeks.

[havocp]

HOCON.md has a section about it but it's probably hard to recognize as relevant if you're looking for the answer to "how do I put a list on the command line." Something more FAQ-like in the README might be nice.