npm package: @rescript-labs/decco
Description: Rescript PPX which generates JSON (de)serializers for user-defined types
Latest version: 2.0.4

# Decco

## Project Status

Decco is lazily maintained by it users, but it's not being actively developed, since its feature set is complete enough for general production use. If you find a major bug that you need fixed, it'll probably be your job to fix it. 💪

## How do I install it?

1. Install package

```
npm i @rescript-labs/decco
```

2. Update your `rescript.json` (or bsconfig.json if you haven't changed its name)

```json
{
  ...,
  "bs-dependencies": [ "@rescript-labs/decco" ],
  "ppx-flags": [ "@rescript-labs/decco/ppx" ],
  ...
}
```

Adding `decco/ppx` to `ppx-flags` will enable the PPX. Adding decco to `bs-dependencies` is required because the code generated by the PPX references the `Decco` module.

## Compatibility

Decco 2.0.0 and above work with ReScript 11 in uncurried mode. If you need to use Decco with an older version of ReScript, install decco version `1.6.0`

If you need to use decco with BuckleScript 5, install `@ryb73/decco` version ^0.1.0 by [following the old ReadMe here](https://github.com/reasonml-labs/decco/blob/0452fc42fa4cd4230d394c718e7f62a0384ce045/README.md).


## What is it?

A Rescript PPX which generates JSON serializers and deserializers for user-defined types.

Example:

```rescript
/* Define types */
@decco type variant<'a> = A | B(int) | C(int, 'a);

type dict = Js.Dict.t<string>;
@decco
type mytype = {
    s: string,
    i: int,
    o: option<int>,
    complex: array<option<list<variant<string>>>>,
    @decco.default(1.0) f: float,
    @decco.key("other_key") otherKey: string,
    magic: @decco.codec(Decco.Codecs.magic) dict,
};

/* Use <typename>_encode to encode */
let encoded = mytype_encode({
    s: "hello",
    i: 12,
    o: None,
    complex: [Some(list{ C(25, "bullseye") })],
    f: 13.,
    otherKey: "other",
    magic: Js.Dict.fromArray([("key","value")]),
});

Js.log(Js.Json.stringifyWithSpace(encoded, 2));
/* {
     "s": "hello",
     "i": 12,
     "o": null,
     "complex": [ [ ["C", 25, "bullseye"] ] ],
     "f": 13,
     "other_key": "other",
     "magic": { "key": "value" }
  } */

/* Use <typename>_decode to decode */
let { s, i, o, complex, f, otherKey, magic } =
    mytype_decode(encoded)->Belt.Result.getExn;
```

## How do I use it?

See the test folder in this repo for some examples.

## Reference

### Attributes

#### @decco

Applies to: type declarations, type signatures

Indicates that an encoder and decoder should be generated for the given type.

#### @decco.encode

Applies to: type declarations, type signatures

Indicates than an encoder (but no decoder) should be generated for the given type.

#### @decco.decode

Applies to: type declarations, type signatures

Indicates than an decoder (but no encoder) should be generated for the given type.

#### @decco.codec

Applies to: type expressions

Specifies custom encoders and decoders for the type. Note that both an encoder and decoder must be specified, even if the type expression is within a type for which @decco.encode or @decco.decode was specified.

```rescript
@decco type t = @decco.codec((fancyEncoder, fancyDecoder)) fancyType;
```

#### @decco.key

Applies to: record fields

By default, ReScript record fields map to JS object fields of the same name. Use @decco.key to specify a custom JS field name. Useful if the JS field name is invalid as a ReScript record field name.

```rescript
@decco
type record = {
    @decco.key("other_key") otherKey: string,
};
```

#### @decco.default

Applies to: record fields
Default: `Js.Json.null`

When decoding a record, the default value will be used for keys that are missing from the JSON object being decoded.

```rescript
@decco type record = {
    @decco.default("def") s: string,
};

let {s} = Js.Json.parseExn("{}")->record_decode->Belt.Result.getExn;
Js.log(s); /* def */
```

# Contributing

Please read the [CONTRIBUTING.md](./CONTRIBUTING.md)