JSON

serde_json works in both directions: to_string / to_string_pretty write, from_str reads. Reading can fail (missing field, wrong type), so it returns a Result:

let k = Kitap { ad: "Dune".into(), yil: 1965 };
let metin = serde_json::to_string(&k)?;
let geri: Kitap = serde_json::from_str(&metin)?;

// for JSON of unknown type
let v: serde_json::Value = serde_json::from_str(r#"{"a":[1,2]}"#)?;
println!("{}", v["a"][1]);   // 2

r#"..."# is a raw string; quotes inside it don't need escaping.

Writing a full JSON parser is a big job; but splitting a flat (non-nested) object is enough to understand what from_str does:

fn duz_oku(json: &str) -> BTreeMap<String, String> {
    json.trim()
        .trim_start_matches('{')
        .trim_end_matches('}')
        .split(',')
        .filter_map(|cift| cift.split_once(':'))
        .map(|(a, d)| (a.trim().trim_matches('"').to_string(),
                       d.trim().trim_matches('"').to_string()))
        .collect()
}

This reader doesn't handle commas inside strings or nested objects; in a real project always use serde_json.