JSON

JavaScript Object Notation (JSON) is a lightweight data-interchange format that is easy for humans to read and write. Furthermore, equally simple for machines to generate and/or parse. JSON is completely language agnostic and that's why it's the ideal interchange format.

To read more about JSON visit: json.org.

Parsing JSON

To parse a JSON string received by another application or generated within your existing application:

import json

struct Customer {
    first_name    string
    last_name     string
    hometown      string
}

fn main() {
    customers_string := '[{ "first_name": "Vitor", "last_name": "Oliveira", "hometown": "Rio de Janeiro" }, { "first_name": "Don", "last_name": "Nisnoni", "hometown": "Kupang" }]'
    customers := json.decode([]Customer, customers_string) or {
        eprintln('Failed to parse json')
        return
    }

    // Print the list of customers
    for customer in customers {
        println('$customer.first_name $customer.last_name: $customer.hometown')
    }
}

Generating JSON

Creating a JSON string for communication or serialization is just as simple. We decode and encode in the example below:

import json

struct Customer {
    first_name    string
    last_name     string
    hometown      string
}

fn main() {
    customer_string := '[{ "first_name": "Vitor", "last_name": "Oliveira", "hometown": "Rio de Janeiro"}]'

    customer := json.decode([]Customer, customer_string) or {
        eprintln('Failed to parse json')
        return
    }

    encoded_json := json.encode(customer)

    println(encoded_json)
}

Exercises

1. Compare how you handle JSON in your favorite language and V.

2. Build an Address struct that contains address information.

3. Use the Address struct to decode and encode a string that contains JSON format.

4. Create 2 structs: Address and User where a user has many addresses. Now receive a string with a nested JSON like '[{ "first_name": "Vitor", "last_name": "Oliveira", "hometown": "Rio de Janeiro", "addresses": [{ street_name: "Rua Princesa Isabel", city: "Rio de Janeiro", country: "Brazil" }] }]', decode and encode it.