Collections aur Standard Library

HashMap<K, V> key-value pairs store karta hai, bilkul Python ke dictionary ya JavaScript ke object ki tarah — lekin key aur value dono types pehle se fixed hone ke sath. [] se indexing karna panic karta hai agar key missing ho, jabki .get() ek Option return karta hai, jisse aap bina crash kiye ek missing key handle kar sakte ho.

use std::collections::HashMap;

fn main() {
    let mut scores: HashMap<String, i32> = HashMap::new();
    scores.insert(String::from("Alice"), 95);
    scores.insert(String::from("Bob"), 87);

    println!("{}", scores["Alice"]);

    if let Some(score) = scores.get("Bob") {
        println!("Bob: {}", score);
    }
}

95
Bob: 87

entry API

entry().or_insert(), Rust ka ek hi step mein update-ya-insert karne ka idiomatic tarika hai: yeh value ka ek mutable reference return karta hai, agar key pehle se waha na ho to pehle ek default insert kar deta hai. contains_key bina kisi Option ko handle kiye ek key ki presence check kar leta hai.

use std::collections::HashMap;

fn main() {
    let mut inventory: HashMap<&str, i32> = HashMap::new();
    inventory.insert("apples", 10);
    inventory.insert("bananas", 5);

    *inventory.entry("apples").or_insert(0) += 3;

    println!("apples: {}", inventory["apples"]);
    println!("has oranges: {}", inventory.contains_key("oranges"));
}

apples: 13
has oranges: false

Yahi Rust ki foundation hai: ownership, borrowing, aur ek type system jo bugs ki poori categories ko runtime surprises ke bajaye compile errors mein badal deta hai. Yahan se, best next step hai practice — ek chhota program pick karo aur use banao, compiler ke error messages par depend karte hue, jo industry ke best messages mein se hain, aapko guide karne ke liye.