Supporting Enum types

[soumyamahunt]

As library is getting more adaption, it is essential to provide support for enum types as well. Currently Swift compiler's way of generating implementation:

{
   "%caseName%": {
    "%%eachArgumentName%%": "%%eachArgumentValue%%",
    "_%%eachArgumentPositionNumer%%": "%%eachArgumentValue%%" // if no argument name
  }
}

For example enum with each case represented in JSON with Swift compiler generated implementation:

enum SomeEnum: Codable {
    /// ```json
    /// {
    ///   "bool": {
    ///     "_0": true
    ///   }
    /// }
    /// ```
    case bool(_ variable: Bool)
    /// ```json
    /// {
    ///   "int": {
    ///     "val": 6
    ///   }
    /// }
    /// ```
    case int(val: Int)
    /// ```json
    /// {
    ///   "string": {
    ///     "_0": "text"
    ///   }
    /// }
    /// ```
    case string(String)
    /// ```json
    /// {
    ///   "multi": {
    ///     "_0":true,
    ///     "_2":"text",
    ///     "val":5
    ///   }
    /// }
    /// ```
    case multi(_ variable: Bool, val: Int, String)
}

I want MetaCodable to behave the same way when enum case argument is provided. Following are the different behavior I have in. mind:

• For cases with _ argument label is provided, argument name will be used rather than current way of using _%argumentPositionNumber. i.e. For the SomeEnum.bool(true) generated JSON with MetaCodable implementation will be:

  {
     "bool": {
        "variable": true
     }
  }

• For cases with single argument and no argument name the value will be directly encoded/decoded rather than being nested with _0 key. i.e. For the SomeEnum.string("text") generated JSON with MetaCodable implementation will be:

  {
     "string":  "text"
  }

• For cases with multiple arguments and some arguments having no name, error will be generated to provide argument name. i.e. The SomeEnum.multi(_ variable: Bool, val: Int, String) will be asked to be changed to SomeEnum.multi(_ variable: Bool, val: Int, strVal: String) or SomeEnum.multi(_ variable: Bool, val: Int, _ strVal: String).

• Additionally MetaCodable will support following dynamic format of JSON:

  [
    {
      "type": "on",
      "onOnlyProperty": "On!"
    },
    {
      "type": "off",
      "offOnlyProperty": "Off!"
    },
  ]

  being represented as Enum:

  enum State: Codable {
    case on(On)
    case off(Off)
  
    struct On: Codable {
      let onOnlyProperty: String
    }
  
    struct Off: Codable {
      let offOnlyProperty: String
    }
  }

Currently attaching macro to case arguments is not supported, which prevents existing features provided by CodedAt, CodedIn, Default and CodedBy being used per enum case arguments. I have raised a request for support here, feel free to provide your reaction and support for this.

Please suggest if you would like anything additional be supported or any changes to be made what has been mentioned here.

[Sajjon]

Nice! I think it would be better if the JSON key was discriminator rather than type, it is more common a term I think.

But perhaps it too, could be customized ?

[soumyamahunt]

Yes the JSON key will be customizable.

[soumyamahunt]

This has been implemented in #48, the only difference being this point:

For cases with multiple arguments and some arguments having no name, error will be generated to provide argument name. i.e. The SomeEnum.multi(_ variable: Bool, val: Int, String) will be asked to be changed to SomeEnum.multi(_ variable: Bool, val: Int, strVal: String) or SomeEnum.multi(_ variable: Bool, val: Int, _ strVal: String).

For such cases, no error will be generated by MetaCodable, for arguments that don't have name they will be directly decoded/encoded to container instead of being keyed.