rustHow to insert an element into a Rust HashMap if it does not already exist?

To insert an element into a Rust HashMap if it does not already exist, the entry API can be used. This API takes a key and a closure as arguments. The closure is called with a mutable reference to the value corresponding to the key, if it exists. The closure can then be used to insert the element if it does not already exist.

Example code

use std::collections::HashMap;

let mut map = HashMap::new();

map.entry("key").or_insert("value");

Output example

()

Code explanation

• entry: API used to insert an element into a Rust HashMap if it does not already exist.
• key: Key of the element to be inserted.
• or_insert: Closure called with a mutable reference to the value corresponding to the key, if it exists.

Helpful links

• Rust HashMap documentation

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