serde

The serde_json crate provides a rich API for interacting with JSON files.

The json macro can be used to serialize any struct decorated with Serialize.

use serde_json::{json, Value};
use serde::{Deserialize, Serialize}; // (1)

#[derive(Debug, Serialize, Deserialize)]
struct Starship {
    name: String,
    registry: String,
    crew: u64
}

fn main() {
    let starship: Starship = Starship{
        name: "USS Enterprise".to_string(), 
        registry: "NCC-1701".to_string(), 
        crew: 400 
    };

    println!("{}", json!("Enterprise": {starship}));
}

1. The derive attributes Serialize and Deserialize are included from serde directly but only after enabling the derive feature (and not the serde_derive crate).

   [dependencies]
   serde = {version = "^1.0", features = ["derive"]}
   

Although a simpler and more naive implementation is possible, the recommended use of the API is to define a struct that reflects the model of the JSON document and to type the destination variable accordingly.

?

There appears to be some bizarre error in the example using &str below.

String&str

#[derive(Debug, serde_derive::Deserialize)]
enum Series {
    TOS,
    DS9,
    VOY,
}

#[derive(Debug, serde_derive::Deserialize)]
struct Starship {
    name: String,
    registry: String,
    series: Series,
}

fn main() {
    let ships: Vec<Starship> = gen_ships("starships.json");
    println!("{:?}", ships);
}

fn gen_ships(fname: &str) -> Vec<Starship> {
    let file = std::fs::read_to_string(&fname).unwrap();
    let ships : Vec<Starship> = serde_json::from_str(&file).unwrap();
    ships
}

#[derive(Debug, serde_derive::Deserialize)]
enum Series {
    TOS,
    DS9,
    VOY,
}

#[derive(Debug, serde_derive::Deserialize)]
struct Starship<'a> {
    name: &'a str,
    registry: &'a str,
    series: Series,
}

fn main() {
    let ships: Vec<Starship> = gen_ships("starships.json");
    println!("{:?}", ships);
}

fn gen_ships(fname: &str) -> Vec<Starship> {
    let file = std::fs::read_to_string(&fname).unwrap();
    let ships : Vec<Starship> = serde_json::from_str(&file).unwrap(); // (1)
    ships
}

1. For some reason, the compiler produces an error here, saying that &file is borrowed. Furthermore the compiler will not allow ships to be returned from the function because it "returns a value referencing data owned by the current function".