What is the difference between policies.route and batteries.forward?

[HPCesia]

Both are used to forward a den class to another class, and their parameters are similar. What exactly is the difference between them? batteries.forward seems more powerful, but policy is a newer thing—which one should I choose?

[theutz]

I would suggest getting used to policies. AFAIK, batteries.forward is implemented with policies now, and is mostly provided for backwards compatibility.

While the battery does look more powerful, that's because a lot of the complexity of it is decomposed into other policy tools, which are significantly more powerful when put together in the long run.

We still need to work up better docs on how it all fits together. But if you have any trouble accomplishing your goals, let us know and we'll help you!

[HPCesia]

I raised this question because of the doc. The Custom Nix Classes section of doc uses batteries.forward as an example instead of policies.

[sini]

We'll update that; thanks for flagging.

[sini]

@HPCesia policies describe relationships; which in essence is what a forward is. They formalize this concept and give us a grammar to link entities and aspects. Policies in fact are much more powerful through composition -- although their actual effects are more atomic in nature. Their full realization will come in the next den kernel iteration that I'm hard at work on.

Den will transition from a resolution stream/simple AST to a fully realized graph.