Read JSON file using from_reader to a struct

---

cargo run ../person.json

examples/json/read-json-from-reader-to-struct/data.json

{
    "fname": "Foo",
    "lname": "Bar",
    "year": 1992,
    "height": 178.2,
    "married": true,
    "numbers": [23, 19, 42],
    "children": [
        {
            "name": "Alpha",
            "birthdate": 2020
        },
        {
            "name": "Beta",
            "birthdate": 2022
        }
    ]
}

examples/json/read-json-from-reader-to-struct/src/main.rs

use serde::Deserialize;
use std::fs::File;

#[derive(Deserialize, Debug)]
struct Person {
    fname: String,
    lname: String,
    married: bool,
}

fn main() {
    let filename = get_filename();

    let data: Person = match File::open(&filename) {
        Ok(file) => serde_json::from_reader(&file).expect("JSON parsing error"),
        Err(error) => {
            eprintln!("Error opening file {}: {}", filename, error);
            std::process::exit(1);
        }
    };
    println!("{:#?}", &data);
    assert_eq!(data.fname, "Foo");
    assert_eq!(data.lname, "Bar");
    assert!(data.married);
}

fn get_filename() -> String {
    let args: Vec<String> = std::env::args().collect();
    if args.len() != 2 {
        eprintln!("Usage: {} FILENAME", args[0]);
        std::process::exit(1);
    }
    args[1].to_owned()
}

Person {
    fname: "Foo",
    lname: "Bar",
    married: true,
}