Scala support

[JannikArndt]

I added scala as an output format.

[schani]

@JannikArndt That's amazing! Thank you.

Do you have plans to support union types eventually?

[schani]

There are a few compile errors:

src/language/Scala.ts(132,26): error TS6138: Property '_packageName' is declared but its value is never read.
src/language/Scala.ts(133,26): error TS6138: Property '_justTypes' is declared but its value is never read.

Also, would you mind adding Scala to the test suite? See languages.ts in test, and the very bottom of fixtures.ts. Basically you'll have to write a little driver program (in test/fixtures/scala) that deserializes JSON and then serializes it back again, and you'll have to tell the test suite how to build and run it. The Dockerfile will also have to install Scala, I guess. Or maybe Maven does that automatically?

[JannikArndt]

Union Types
There is no obvious and universal way to represent union types in Scala (that's the beauty of the language 😉). A colleague of mine suggested nested Either (okay for two types, ugly for more) or shapeless' hlist, which would add another dependency.
So to answer your question, if I plan to support union types eventually: If I find an adequate solution, I will definitely add it, but I'd rather not support them then add a somewhat broken support. And I am still tinkering with possible solutions.

Tests
Yeah, I did see that one coming when I looked at #838 😉 It's on my list.

Compile warnings
Fixed that 👍

[schani]

I thought cases classes is how you represent unions in Scala? Isn't that the equivalent to discriminated unions in ML-like languages?

We'll wait for the test suite before merging.

[schani]

Btw, if you need any help, it's probably quicker if you join us on Slack.

[schani]

@JannikArndt What's the status on this? Can we help?

[JannikArndt]

Hey there, sorry, I didn't have the time to write the tests, yet :(

[hderms]

@JannikArndt is there anything wrong with just having a sealed trait of one argument case classes to represent union types? I suppose it would play weird with singleton types like None or something so I suppose that partially answers the question.

Dotty won't become Scala 3 until 2020 as far as I've heard, so I feel like there are precious limited options in the short term.

[hderms]

@JannikArndt any opposition to handling this like https://scalapb.github.io/generated-code.html

specifically the section on oneOf?

[JannikArndt]

@hderms Sounds good, I personally like the ScalaPB style. I still didn't find the time to implement anything further, though :(

[schani]

@JannikArndt @hderms I'd really like to get this closed. I'm happy to take over the work if you can give a short summary of what still needs to be done, from your point of view. If you could write a test driver (see test/fixtures/* for other language's drivers) I'd be much obliged, but I can figure it out myself if you don't have the time at all.

[hderms]

@schani I'm not sure what needs to be done still but I felt like imitating the way ScalaPB does union types would be a reasonable way to do oneOf

[schani]

Doesn't look like this is moving forward, so I'm closing it for now. Please revive when/if there is new work.

[hderms]

@schani I'm working on this now. Can you point me in the direction of a json schema or whatever that we would be expected to produce unions from? I tried test/inputs/schema/direct-union.1.json and test/inputs/schema/union.json and neither seem to produce unions in either Kotlin or Rust. Maybe those languages don't implement unions properly or am i incorrect in thinking these files should produce union'd types?

[schani]

@hderms Kotlin does not produce unions, but Rust does. It doesn't look like much in Rust, but that's because Rust's serialization framework does all the hard work. To see how to do it the hard way, look at C#, Swift, or Go.

[hderms]

@schani maybe I'm misinterpreting it but I don't get how this output is a union?

npm start -- "--lang csharp test/inputs/schema/union.schema"

> quicktype@15.0.0 start /Users/dermothaughey/projects/quicktype
> script/watch "--lang csharp test/inputs/schema/union.schema"

> Watching src/
// <auto-generated />
//
// To parse this JSON data, add NuGet 'Newtonsoft.Json' then do:
//
//    using QuickType;
//
//    var union = Union.FromJson(jsonString);

namespace QuickType
{
    using System;
    using System.Collections.Generic;

    using System.Globalization;
    using Newtonsoft.Json;
    using Newtonsoft.Json.Converters;

    public partial class Union
    {
        [JsonProperty("$schema")]
        public Uri Schema { get; set; }

        [JsonProperty("type")]
        public string Type { get; set; }

        [JsonProperty("items")]
        public Items Items { get; set; }
    }

    public partial class Items
    {
        [JsonProperty("oneOf")]
        public OneOf[] OneOf { get; set; }
    }

    public partial class OneOf
    {
        [JsonProperty("type")]
        public string Type { get; set; }

        [JsonProperty("properties")]
        public Properties Properties { get; set; }

        [JsonProperty("required")]
        public string[] OneOfRequired { get; set; }
    }

    public partial class Properties
    {
        [JsonProperty("one", NullValueHandling = NullValueHandling.Ignore)]
        public One One { get; set; }

        [JsonProperty("two")]
        public One Two { get; set; }

        [JsonProperty("three", NullValueHandling = NullValueHandling.Ignore)]
        public One Three { get; set; }
    }

    public partial class One
    {
        [JsonProperty("type")]
        public string Type { get; set; }
    }

    public partial class Union
    {
        public static Union FromJson(string json) => JsonConvert.DeserializeObject<Union>(json, QuickType.Converter.Settings);
    }

    public static class Serialize
    {
        public static string ToJson(this Union self) => JsonConvert.SerializeObject(self, QuickType.Converter.Settings);
    }

    internal static class Converter
    {
        public static readonly JsonSerializerSettings Settings = new JsonSerializerSettings
        {
            MetadataPropertyHandling = MetadataPropertyHandling.Ignore,
            DateParseHandling = DateParseHandling.None,
            Converters =
            {
                new IsoDateTimeConverter { DateTimeStyles = DateTimeStyles.AssumeUniversal }
            },
        };
    }
}

or this:

package main

import "encoding/json"

func UnmarshalUnion(data []byte) (Union, error) {
	var r Union
	err := json.Unmarshal(data, &r)
	return r, err
}

func (r *Union) Marshal() ([]byte, error) {
	return json.Marshal(r)
}

type Union struct {
	Schema string `json:"$schema"`
	Type   string `json:"type"`
	Items  Items  `json:"items"`
}

type Items struct {
	OneOf []OneOf `json:"oneOf"`
}

type OneOf struct {
	Type       string     `json:"type"`
	Properties Properties `json:"properties"`
	Required   []string   `json:"required"`
}

type Properties struct {
	One   *One `json:"one,omitempty"`
	Two   One  `json:"two"`
	Three *One `json:"three,omitempty"`
}

type One struct {
	Type string `json:"type"`
}

is union.schema expected to output an actual union type?

[schani]

Sorry, you'll have to pass --src-lang schema

[hderms]

@schani my bad. That's what I get for trying to work on a project I barely understand :)

[schani]

We're also somewhat lacking in the documentation department ;-)