Assign value if not exist in Rust 1.55

In Rust 1.55, we can use the or_insert() method of the std::collections::HashMap to assign a value if it doesn't already exist.

Here's an example:

``rust use std::collections::HashMap;


// create a new hashmap

let mut my_map = HashMap::new();
// using or_insert() to assign a value if it doesn't already exist

my_map.entry("Key1").or_insert(10);

my_map.entry("Key2").or_insert(20);
// print the values

println!("Value of Key1: {:?}", my_map.get("Key1"));

println!("Value of Key2: {:?}", my_map.get("Key2"));



In this example, we create a new HashMap called my_map, and then use the or_insert() method to add values if the key doesn't already exist. We use the entry() method to get the value associated with a key. If the key doesn't exist, or_insert() inserts the given value into the map and returns a mutable reference to the value.
You can also use a closure with or_insert() to specify how to create the value if it doesn't exist. Here's an example:

 rust

let mut my_map = HashMap::new();
// using closure with or_insert() to assign a value if it doesn't already exist

my_map.entry(3).or_insert_with(|| vec![1, 2, 3]);

// print the value println!("Value: {:?}", my_map.get(&3));`

In this example, we use the or_insert_with() method with a closure that returns a new Vec` containing the values 1, 2, and 3. This closure is only called if the key doesn't already exist in the map.

I hope this helps! Let me know if you have any other questions.

Assign value if not exist in Rust 1.55

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