1. Open the Cargo.toml file that was generated earlier for you

2. Under [dependencies], if you haven't done so already, add the following line:

serde_json = "1.0.8"

3. If you want, you can go to the serde_json crates.io web page (https://crates.io/crates/serde_json) to check for the newest version and use that one instead

4. In the bin folder, create a file called dynamic_json.rs

5. Add the following code and run it with cargo run --bin dynamic_json:

1    #[macro_use] 
2    extern crate serde_json;
3 
4    use std::io::{self, BufRead};
5    use std::collections::HashMap;
6 
7    fn main() {
8      // A HashMap is the same as a JSON without any schema
9      let mut key_value_map = HashMap::new();
10     let stdin = io::stdin();
11     println!("Enter a key and a value");
12     for input in stdin.lock().lines() {
13       let input = input.expect("Failed to read line");
14       let key_value: Vec<_> = input.split_whitespace().collect();
15       let key = key_value[0].to_string();
16       let value = key_value[1].to_string();
17 
18       println!("Saving key-value pair: {} -> {}", key, value);
19       // The json! macro lets us convert a value into its JSON 
            representation
20       key_value_map.insert(key, json!(value));
21       println!(
22         "Enter another pair or stop by pressing '{}'",
23          END_OF_TRANSMISSION
24       );
25     }
26     // to_string_pretty returns a JSON with nicely readable 
          whitespace
27     let json =
28     serde_json::to_string_pretty(&key_value_map).expect("Failed 
       to convert HashMap into JSON");
29     println!("Your input has been made into the following 
       JSON:");
30     println!("{}", json);
31   }
32 
33   #[cfg(target_os = "windows")]
34   const END_OF_TRANSMISSION: &str = "Ctrl Z";
35 
36   #[cfg(not(target_os = "windows"))]
37   const END_OF_TRANSMISSION: &str = "Ctrl D";