0001-explicit-encode-function-on-validator-enum.md

1. Explicit encode function on Validator.Enum

Date: 2019-10-03

Context

To represent enum values in documentation, we need a way to encode them into appropriate raw values. However, codecs and validators are created independently. The codec, to which a validator is added, can be a mapped codec, a product, etc.

As codecs are opaque (at least for now), given a codec we don't necessarily have a codec for the wrapped types or fields. Hence, even given a codec, we don't necessarily have an encode method for the value.

Decision

As proposed in PR240, the Enum class will now contain an explicit encode function:

case class Enum[T](possibleValues: List[T], encode: Option[EncodeToAny[T]])

It might seem that another solution would be to require an implicit Codec instance when creating the enum validator, however validators are often created as part of codec creation; this would create an infinite loop, e.g.:

implicit def plainCodecForColor: PlainCodec[Color] = {
  Codec.stringPlainCodecUtf8
    .map[Color]({
       case "red"  => Red
       case "blue" => Blue
    })(_.toString.toLowerCase)
    .validate(Validator.enum)
}