https://github.com/ahrefs/ppx_deriving_atd

https://github.com/ahrefs/ppx_deriving_atd

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• Host: GitHub
• URL: https://github.com/ahrefs/ppx_deriving_atd
• Owner: ahrefs
• Created: 2024-09-05T19:19:44.000Z (4 months ago)
• Default Branch: master
• Last Pushed: 2024-09-05T20:07:37.000Z (4 months ago)
• Last Synced: 2024-12-16T19:17:43.398Z (24 days ago)
• Language: OCaml
• Size: 42 KB
• Stars: 0
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# ppx\_deriving\_atd

## Overview

This package introduces a PPX (Preprocessor Extension) for OCaml that automates the generation of serialization and deserialization functions for your OCaml types using [ATD](https://github.com/ahrefs/atd) without creating an ATD file.  

Currently supporting JSON derivation only:

- `json_string_of_t`: Serializes an OCaml value to a JSON string.

- `t_of_json_string`: Deserializes a JSON string back into an OCaml value.

## Usage

```ocaml

type my_type = {

  field1: string;

  field2: int;

} [@@deriving atd_j]

(* Serialization *)

let my_value = { field1 = "value1"; field2 = 123 }

let json_string = json_string_of_my_type my_value (* {"field1":"value1","field2":123} *)

(* Deserialization *)

let deserialized_value = my_type_of_json_string json_string

```

### Supported Annoations

#### default

Annotating a record field with `[@default v]` will allow the generated reader to give default value for the field (and so the field no longer have an optional type).  Note `v` must be in a stringify form: `"999"` instead of `999`.

```ocaml

type my_type = {

  field1: string;

  field2: int [@default "999"];

} [@@deriving atd_j]

(* Deserialization *)

let deserialized_value = my_type_of_json_string {|{"field1":"value1"}|}

(* { field1 = "value1"; field2 = 999 } *)

```

#### required

All option typed fields are "optional" by default, i.e. if the value is `None`, it will not be included when serialization and when deserializing, ATD will assume the value is `None` if the field is not present.  

Annotating a record field with `[@required]` will always keep the optional value in the serialized record and ATD will keep looking for it when deserializing the records.

```ocaml

type my_type = {

  field1: string option;

  field2: int option [@required];

} [@@deriving atd_j]

(* Serialization *)

let my_value = { field1 = None; field2 = None }

let json_string = json_string_of_my_type my_value (* {"field2":"None"} *)

(* Deserialization *)

let deserialized_value = my_type_of_json_string "{}"

(* Fatal error: exception Atdgen_runtime.Oj_run.Error("Line 1:\nMissing record field field2") *)

```