v/vlib/x/json2/README.md

> `json2` was named just to avoid any unwanted potential conflicts with the existing codegen tailored for the main `json` module which is powered by CJSON.

An experimental version of the JSON parser written from scratch on V. 

## Usage
```v
import x.json2
import http

fn main() {
    // Decoding
    resp := http.get('https://example.com')?

    // raw decode
    raw_person := json2.raw_decode(resp.text)?

    // Casting `Any` type / Navigating
    person := raw_person.as_map()
    name := person['name'].str() // Bob
    age := person['age'].int() // 19
    pi := person['pi'].f64() // 3.14.... 

    // Constructing an `Any` type
    mut me := map[string]json2.Any
    me['name'] = 'Bob'
    me['age'] = 18

    mut arr := []json2.Any
    arr << 'rock'
    arr << 'papers'
    arr << json2.null()
    arr << 12

    me['interests'] = arr

    mut pets := map[string]json2.Any
    pets['Sam'] = 'Maltese Shitzu' 
    me['pets'] = pets

    // Stringify to JSON
    println(me.str())
    //{"name":"Bob","age":18,"interests":["rock","papers","scissors",null,12],"pets":{"Sam":"Maltese"}}

    // Encode a struct/type to JSON
    encoded_json := json2.encode<Person>(person2)
}
```
## Using `decode<T>` and `encode<T>`
> Codegen for this feature is still WIP. You need to manually define the methods before using the module to structs.

In order to use the `decode<T>` and `encode<T>` function, you need to explicitly define two methods: `from_json` and `to_json`. `from_json` accepts a `json2.Any` argument and inside of it you need to map the fields you're going to put into the type. As for `to_json` method, you just need to map the values into `json2.Any` and turn it into a string.

```v
struct Person {
mut:
    name string
    age  int = 20
    pets []string
}

fn (mut p Person) from_json(f json2.Any) {
    obj := f.as_map()
    for k, v in obj {
        match k {
            'name' { p.name = v.str() }
            'age' { p.age = v.int() }
            'pets' { p.pets = v.arr().map(it.str()) }
            else {}
        }
    }
}

fn (p Person) to_json() string {
    mut obj := map[string]json2.Any
    obj['name'] = p.name
    obj['age'] = p.age
    obj['pets'] = p.pets
    return obj.str()
}

fn main() {
    resp := os.read_file('./person.json')?
    person := json2.decode<Person>(resp)
    println(person) // Person{name: 'Bob', age: 28, pets: ['Floof']}
    person_json := json2.encode<Person>(person)
    println(person_json) // {"name": "Bob", "age": 28, "pets": ["Floof"]}
}
```

## Using struct tags
`x.json2` cannot use struct tags just like when you use the `json` module. However, it emits an `Any` type when decoding so it can be flexible on the way you use it.

### Null Values
`x.json2` have a `null` value for differentiating an undefined value and a null value. Use `is` for verifying the field you're using is a null.

```v
fn (mut p Person) from_json(f json2.Any) {
    obj := f.as_map()
    if obj['age'] is json2.Null {
        // use a default value
        p.age = 10
    }
}
```

### Custom field names
In `json`, you can specify the field name you're mapping into the struct field by specifying a `json:` tag. In `x.json2`, just simply cast the base field into a map (`as_map()`) and get the value of the field you wish to put into the struct/type.

```v
fn (mut p Person) from_json(f json2.Any) {
    obj := f.as_map()
    p.name = obj['nickname'].str()
}
```

```v
fn (mut p Person) to_json() string {
    obj := f.as_map()
    obj['nickname'] = p.name
    return obj.str()
}
```

### Undefined Values
Getting undefined values has the same behavior as regular V types. If you're casting a base field into `map[string]json2.Any` and fetch an undefined entry/value, it simply returns empty. As for the `[]json2.Any`, it returns an index error.

## Casting a value to an incompatible type
`x.json2` provides methods for turning `Any` types into usable types. The following list shows the possible outputs when casting a value to an incompatible type.

1. Casting non-array values as array (`arr()`) will return an array with the value as the content.
2. Casting non-map values as map (`as_map()`) will return a map with the value as the content.
3. Casting non-string values to string (`str()`) will return the stringified representation of the value.
4. Casting non-numeric values to int/float (`int()`/`f64()`) will return zero.