Add default wrapper

[treeowl]

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newtype DefaultJSON a = DefaultJSON a

instance (Generic a, GToJSON Zero (Rep a), GToEncoding Zero (Rep a))
    => ToJSON (DefaultJSON a) where
  toJSON (DefaultJSON a) = genericToJSON defaultOptions a
  toEncoding (DefaultJSON a) = genericToEncoding defaultOptions a

instance (Generic a, GFromJSON Zero (Rep a)) => FromJSON (DefaultJSON a) where
  parseJSON x = DefaultJSON <$> genericParseJSON defaultOptions x

This can be used with DerivingVia:

data Message val = Message {val :: val, teamId :: Int, messageType :: Char}
  deriving Generic
  deriving (ToJSON, FromJSON) via DefaultJSON (Message val)

This is almost as easy as writing empty instances, but it includes the toEncoding optimization for ToJSON.

[bergmark]

Looks nice 👍

[treeowl]

There's an active proposal (by Alexis King) to add Generically to base. We might be better off waiting to see if that happens, and use it if so.

[phadej]

Looks like Generically isn't happening. I'll add something to aeson in meanwhile.

[phadej]

@bergmark What you think, what would be better module name to include this (and e.g. DotNetTime and others types).

• Data.Aeson.Deriving
• Data.Aeson.Newtypes

or something else?

[bergmark]

I like .Deriving for this one and other helpers. For DotNetTime and friends I'd like a name that reflects the use case, not how they are implemented (shouldn't matter if DotNetTime is derived, a newtype, or written manually). Data.Aeson.Types is taken :-S Data.Aeson.Data might be too generic.Data.Aeson.JSONTypes (also generic... edit: and misleading, these are not defined in the json spec)?

[amesgen]

I think this can be closed as an instance as suggested above was added for Generically in #951 and released in 2.1.0.0.