jsonizer 0.0.2

Flexible JSON serializer requiring minimal boilerplate

To use this package, run the following command in your project's root directory:

Manual usage
Put the following dependency into your project's dependences section:

jsonizer: D language JSON serializer

The primary purpose of jsonizer is to automate the generation of methods needed to serialize and deserialize user-defined D structs and classes from JSON data. jsonizer is not a standalone json parser, but rather a convenience layer on top of std.json, allowing you to more easily work with JSONValue objects.

To use jsonizer, the main components you ened to be aware of are the methods extract!T and toJSON, the attribute @jsonize, and the mixin template JsonizeMe.


extract!T is jsonizer's utility knife for converting a JSONValue to an object of type T. Given a JSONValue json

JSONValue json; // lets assume this has some data in it
int i             = json.extract!int;
MyEnum e          = json.extract!MyEnum;
MyStruct[] s      = json.extract!(MyStruct[]);
MyClass[string] c = json.extract!(MyClass[string]);

extract!T will fail (with enforce) if the json object's type is not something it knows how to convert to T.

For primitive types, extract leans on the side of flexibility -- for example, extract!int on a json entry of type string will try to parse an int from the string.

For user-defined types, you have to do a little work to set up your struct or class for jsonizer.

@jsonize and JsonizeMe

The simplest way to make your type support json serialization is to mark its members with the @jsonize attribute and have mixin JsonizeMe; somewhere in your type definition. For example:

struct S {
  mixin JsonizeMe; // this is required to support jsonization

  @jsonize { // public serialized members
    int x;
    float f;
  string dontJsonMe; // jsonizer won't touch members not marked with @jsonize

The above could be deserialized by calling extract!S from a json object like:

{ "x": 5, "f": 1.2 }

This is a good place to note that jsonize will not error if a member was not specified in the json object, nor would it error if some extraneous key was present.

Your struct could be converted back into a JSONValue by calling toJSON on an instance of it.

jsonizer can do more than just convert public members though:

struct S {
  mixin JsonizeMe; // this is required to support jsonization

  // jsonize can convert private members too.
  // by default, jsonizer looks for a key in the json matching the member name
  // you can change this by passing a string to @jsonize
  private @jsonize("f") float _f;

  // you can use properties for more complex serialization
  // this is useful for converting types that are non-primitive
  // but also not defined by you, like std.datetime's Date
  private Date _date;
  @property @jsonize {
    string date() { return dateToString(_date); }
    void date(string str) { _date = dateFromString(str); }

Assuming dateToString and dateFromString are some functions you defined, the above could be extracted from a json object looking like:

{ "f": 2.1, "date": "2015-05-01" }

The above examples work on both classes and structs provided the following:

  1. Your type mixes in JsonizeMe
  2. Your members are marked with @jsonize
  3. Your type has a no-args constructor

jsonized constructors

In some cases, #3 above may not seem so great. What if your type needs to support serialization but shouldn't have a default constructor? In this case, you want to @jsonize your constructor:

class Custom {
  mixin JsonizeMe;

  @jsonize this(int i, string s = "hello") {
    _i = i;
    _s = s;

  @jsonize("i") int    _i;
  @jsonize("s") string _s;

Given a type T with one or more constructors tagged with @jsonize, extract!T will try to match the member names and types to a constructor and invoke that with the corresponding values from the json object. Parameters with default values are considered optional; if they are not found in the json, the default value will be used. The above example could be constructed from json looking like:

{ "i": 5, "s": "hi" }

If "s" were not present, it would be assigned the value "hello".

Note that while you can @jsonize multiple constructors, there should be no overlap between situations that could satisfy them. If a given json object could possibly match multiple constructors, jsonizer chooses arbitrarily (it does not attempt to pick the 'most appropriate' constructor).

The method of jsonizing your constructor is also useful for types that need to perform a more complex setup sequence.

Also note that when using @jsonize constructors, mixing in JsonizeMe and marking members with @jsonize are only necessary for serialization -- if your object only needs to support deserialization, marking a constructor is sufficient.

factory construction

This is one of the newer and least tested features of jsonizer. Suppose you have the following classes:

module test;
class TestComponent {
  mixin JsonizeMe;
  @jsonize int c;

class TestCompA : TestComponent {
  mixin JsonizeMe;
  @jsonize int a;

class TestCompB : TestComponent {
  mixin JsonizeMe;
  @jsonize string b;

and the following json:

    "class": "test.TestCompA",
     "c": 1,
     "a": 5
    "class": "test.TestCompB",
    "c": 2,
    "b": "hello"

Calling extract!(TestComponent[]) on a JSONValue parsed from the above json string should yield a TestComponent[] of length 2. While both have the static type TestComponent, one is actually a TestCompA and the other is a TestCompB, both with their fields appropriately populated.

Behind the scenes, jsonizer looks for a special key 'class' in the json (chosen because class is a D keyword and could not be a member of your type). If it finds this, it calls Object.factory using the specified string. It then calls populateFromJSON, which is a method generated by the JsonizeMe mixin.

For this to work, your type must:

  1. Have a default constructor
  2. mixin JsonizeMe in every class in the hierarchy
  • rcorre
0.7.7 2022-Jan-06
0.7.6 2018-Jul-08
0.7.5 2018-Mar-27
0.7.4 2017-Aug-05
0.7.3 2016-Nov-27
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