Add DataClass Hydra Support

[SeanNaren]

Related #37

The final piece is to add automatic defaults + type checking for dataclasses.

Two options:

• Via the ConfigStore: https://hydra.cc/docs/next/tutorials/structured_config/schema/ which would need to store all configs that we'd like to type check/duck-type via Hydra. The object remains a DictConfig (duck-typing)
• Carlos Idea: provide a _name_ within the config to automatically convert to a specific data-class, go through the tree recursively

Choice 1 is closer to Hydra, Choice 2 is better because we actually pass data-classes around.

[carmocca]

Choice 2 recap:

• You cant mix DictConfigs and dataclasses. The later will be converted: Setting non-dictconfig attributes omry/omegaconf#480
• This means we cant use any DictConfigs. this forces to either use all dataclasses or introducing a third structure like argparse.Namespace. We chose the first option
• There is no such thing as a dataclass that allows **kwargs. I hacked one myself but there is no easy way to set its types.
• dataclass.fields() does not return non-typed fields. This in turn makes OmegaConf.structured not work: OmegaConf.structured does not parse dataclass attributes which are not typed omry/omegaconf#489
• Even if you get all of this to work, instantiate(dataclass) will convert it back to a DictConfig so we didn't achieve anything.
• Also, instantiate does not support Union types, so forget about adding them to your dataclasses.

So looks like we'll have to marry DictConfig or scrap Hydra...

[SeanNaren]

I've seen a few repos that have Hydra in place: https://github.com/facebookresearch/mmf

That might be a good place to have a look as to how things have been integrated there as well

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[omry]

OmegaConf 2.1 can now convert the config to real dataclasses:

https://omegaconf.readthedocs.io/en/latest/usage.html#omegaconf-to-object

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.