std::collections::HashMap

An associative array type using hash tables, storing key-value pairs with fast lookup and insert operations.

See Examples

When to Use HashMap

Use HashMap when you need fast lookups and insertions with arbitrary keys. It's ideal for caching, configuration storage, and dynamic key-value scenarios where hash-based access outperforms ordered collections.

Performance Characteristics

O(1) Average

Insert

O(1) Average

Lookup

O(n) Memory

Storage

Worst-case performance can degrade to O(n) for poor hash functions. Use high-quality hashers for production workloads.

Example Usage


use std::collections::HashMap;

fn main() {
    let mut map = HashMap::new();
    
    map.insert("key1", 42);
    map.insert("key2", 24);
    
    // Retrieve a value
    if let Some(value) = map.get("key1") {
        println!("Value: {}", value);
    }
    
    // Check if a key exists
    if !map.contains_key("key3") {
        println!("Key not found");
    }
}

Best Practices