rustHow to use a custom hasher with a Rust HashMap?

Using a custom hasher with a Rust HashMap is easy. You can define a custom hasher by implementing the BuildHasher trait. Then you can pass the hasher to the HashMap constructor.

use std::collections::HashMap;
use std::hash::{BuildHasher, Hasher};

struct MyHasher;

impl BuildHasher for MyHasher {
    type Hasher = MyHasher;

    fn build_hasher(&self) -> Self::Hasher {
        MyHasher
    }
}

impl Hasher for MyHasher {
    fn finish(&self) -> u64 {
        0
    }

    fn write(&mut self, _bytes: &[u8]) {
        // Do nothing
    }
}

let mut map: HashMap<&str, &str, MyHasher> = HashMap::with_hasher(MyHasher);
map.insert("foo", "bar");

assert_eq!(map.get("foo"), Some(&"bar"));

The code above defines a custom hasher MyHasher and uses it to create a HashMap.

1. MyHasher implements the BuildHasher trait, which provides the build_hasher method.
2. MyHasher also implements the Hasher trait, which provides the finish and write methods.
3. The HashMap constructor is called with MyHasher as the hasher.
4. The insert method is used to add a key-value pair to the HashMap.
5. The get method is used to retrieve the value associated with the key.

Helpful links

• Rust HashMap Documentation
• Rust BuildHasher Trait Documentation
• Rust Hasher Trait Documentation

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