Hashmaps

Rust also provides us with maps, which can be used to store key-value data. They come from the std::collections module and are named HashMap. They are created with the HashMap::new constructor function:

// hashmaps.rs

use std::collections::HashMap; 

fn main() { 
    let mut fruits = HashMap::new(); 
    fruits.insert("apple", 3);
    fruits.insert("mango", 6);
    fruits.insert("orange", 2);
    fruits.insert("avocado", 7);
    for (k, v) in &fruits {
        println!("I got {} {}", v, k);
    }

    fruits.remove("orange");
    let old_avocado = fruits["avocado"];
    fruits.insert("avocado", old_avocado + 5);
    println!("\nI now have {} avocados", fruits["avocado"]);
}

In the preceding code, we created a new HashMap called fruits. We then insert some fruits into our fruits map, along with their count, using the insert method. Following that, we iterate over the key value pairs using for loop, where in we take a reference to our fruit map by &fruits, because we only want read access to the key and value. By default, the value will be consumed by the for loop. The for loop in this case returns a two field tuple ((k ,v)). There are also seperate methods keys() and values() available to iterate over just keys and values, respectively. The hashing algorithm used for hashing the keys of the HashMap type is based on the Robin hood open addressing scheme, but can be replaced with a custom hasher depending on the use case and performance. That's about it.

Next, let's look at slices.