8. HashMaps

hashmaps.md

8. HashMaps

• Construction, insertion
• Lookup, deletion
• Matching
• HashMap literals

Construction, insertion

use std::collections::HashMap;

fn main() {
    let mut m : HashMap<String, u64> = HashMap::new();
    m.insert("abc".to_string(), 12);
    m.insert("xyz".to_string(), 13);
    println!("{:?}", m);
}

use std::collections::HashMap;

fn main() {
    let mut m : HashMap<String, u64> = HashMap::with_capacity(3);
    m.insert("abc".to_string(), 12);
    m.insert("xyz".to_string(), 13);
    println!("{:?}", m);
}

use std::collections::HashMap;

fn main() {
    let mut m : HashMap<String, u64> = HashMap::with_capacity(3);
    let x = m.insert("abc".to_string(), 12);
    println!("{:?}", x);
    m.insert("xyz".to_string(), 13);
    let y = m.insert("abc".to_string(), 13);
    println!("{:?}", y);
    println!("{:?}", m);
}

Lookup, deletion

use std::collections::HashMap;

fn main() {
    let mut m : HashMap<String, u64> = HashMap::new();
    m.insert("abc".to_string(), 12);
    m.insert("xyz".to_string(), 13);
    println!("{:?}", m);
    let key = "abc".to_string();
    let x = m.get(&key);
    println!("{:?}", x);
    let y = m.remove(&key);
    println!("{:?}", y);
    println!("{:?}", m);
    let x = m.get(&key);
    println!("{:?}", x);
}

Matching

use std::collections::HashMap;

fn main() {
    let mut m : HashMap<String, u64> = HashMap::new();
    m.insert("abc".to_string(), 12);
    m.insert("xyz".to_string(), 13);
    println!("{:?}", m);

    let key = "abc".to_string();
    let x = m.get(&key);
    match x {
        Some(xx) => println!("Found {}", xx),
        None => println!("Not found!"),
    };

    let y = m.remove(&key);
    println!("{:?}", y);
    println!("{:?}", m);

    let x = m.get(&key);
    match x {
        Some(xx) => println!("Found {}", xx),
        None => println!("Not found!"),
    };
}

HashMap literals

use std::collections::HashMap;

fn main() {
    let m = HashMap::from([("abc".to_string(), 12), ("xyz".to_string(), 13)]);      println!("{:?}", m);
}

References:

• Rust book: https://doc.rust-lang.org/book/ch08-03-hash-maps.html
• Video: https://youtu.be/IAegWSWCjcM
• Overview: https://gist.github.com/max-itzpapalotl/18f7675a60f6f9603250367bcb63992e