Circe: Privileged configurable generic derivation

[dwijnand]

From your post https://meta.plasm.us/posts/2016/01/14/configuring-generic-derivation/

I was wondering if perhaps in a codebase, where there is a set convention (in my case snake_case over camelCase keys), it would be possible to configure that the priviledged .asJson to would always mean use SnakeCaseKeys, and do the same also for the decoding API.

[travisbrown]

It's possible to do this now:

import io.circe._, io.circe.generic.auto._, io.circe.generic.config._

implicit def snakeCaseDecoder[A](implicit
  decoder: ConfiguredDecoder[SnakeCaseKeys, A]
): export.Export0[Decoder[A]] = new export.Export0(decoder)

This exports instances configured to use snake-case at a higher priority that the default for exported instances. These won't take priority over custom instances, but they do outrank the default unconfigured derived instances.

(Note that this is just a demonstration—in real code you'd probably want to define something like a SnakeCaseDecoder subclass of Decoder and export instances with @exports(HighPriority)).

[dwijnand]

That's awesome, especially the priority over custom instances part. Thank you.

[travisbrown]

I'm going to reopen this issue because I can imagine providing explicit support for this—e.g. something like:

import io.circe.generic._, io.circe.generic.config._

val deriver: ConfiguredDeriver[SnakeCaseKeys] = ConfiguredDeriver[SnakeCaseKeys]

import deriver._

I'm not 100% sure I like this, but I think it's worth discussing.

[onsails]

That would be great to be able to make the whole scope to use snake case keys because usually APIs accept keys encoded in exactly one style.

[dwijnand]

Using a package object at the root and declaring the package as such:

package myrootpackage
package foo