Feature - set config values by path

[danieleades]

i see that it's possible to extract values from configuration using a period-delimited 'path' str. Is there anyway to do the inverse operation? That is, set a nested value using the path to the key.

The use case i'm envisaging is that

• most of the config for the application will be set in a configuration file, with some nesting
• a user should be able to override every value in the file if they wish

I had imagined an interface like

APP --config path.to.key=value

what's the best way to approach this using your library?

[Techcable]

Ideally, it would be style-preserving too 😄

[SergioBenitez]

That is, set a nested value using the path to the key.

Yes. This is the way string keys work everywhere. See the Serialized provider docs as an example. For instance, (key, value), built using Serialize, works as expected. That is, figment.merge(("a.b", 12)) replaces b in a with 12.

what's the best way to approach this using your library?

Parse the CLI value(s) using something like clap, then simply do something like:

// The value can be anything `Serialize`. `figment::value::Value` is a good choice.
let overrides: Vec<(String, figment::value::Value)> = /* result from CLI parsing */;
let mut figment = /* whatever your figment looks like */;
for override in overrides {
    figment = figment.merge(override);
}

You can even add provenance information to these CLI values by implementing a custom provider, which will give you perfect error messages should something go wrong, but it's not required.

[danieleades]

ah nice, that's quite powerful. Did I miss this in the docs?

[SergioBenitez]

It is documented, though perhaps not as well as it should be. I've added this detail to more places in the docs.