feature: unmarshal with defaults and required fields

[thnk2wn]

It'd be great to have required and default attribute support when unmarshalling koanf config into structs.

While it might not be the primary focus of koanf, I think that unmarshalling config into structs is the primary way most want to reference the config values koanf holds.

Ensuring required configuration items are set and providing reasonable defaults when they're not is very common and we're used to the support from modules like kelseyhightower/envconfig. Without that there's a lot more tedious work to do before and after koanf loading.

I took a quick stab at merging this functionality from kelseyhightower/envconfig into a new unmarshal method in our forked repo. While it's only been quickly tested, the envconfig source is rock solid and I minimized changes for quick start. The performance could probably be improved. At any rate, it's here for reference if it's helpful for the feature intent and/or potential future implementation.

teamjobot/koanf/pull/2

[qianlongzt]

Try using https://github.com/go-playground/validator for validation.

Use go value for defaults

var config *Config = &Config{
    Port: "8989",
}

type Config struct {
    Port string 
}

k.UnmarshalWithConf("", config, koanf.UnmarshalConf{Tag: "tag"})

[thnk2wn]

@qianlongzt Thanks. I'm not sure that defaults approach works when doing things like generics and dynamically creating. Validator probably works for validation though it's probably overkill and one extra step and dependency.

[OhohLeo]

Hello @thnk2wn, Do you know when next release is planned ?
This default & required feature would be greatly appreciated!
Thanks.

[thnk2wn]

@OhohLeo I'm not a maintainer of this project, was just trying to help a bit with one issue and this question.

I believe the position for this project is as @qianlongzt mentioned above

You could certainly try the defaults and required behavior I added using my forked version at https://github.com/teamjobot/koanf but I'm not sure if we'll maintain that yet so it may grow stale or you might run into bugs with the changes.