Vec & HashMap in Rust
From the Rust cheat sheet · Collections & Iterators · verified Jul 2026
Vec & HashMap
Dynamic arrays and key-value maps.
rust
// Vec — dynamic array
let mut v = vec![1, 2, 3];
v.push(4);
v.pop(); // Some(4)
let first = &v[0]; // Panics if out of bounds
let first = v.get(0); // Returns Option<&T>
// HashMap
use std::collections::HashMap;
let mut map = HashMap::new();
map.insert("Alice", 30);
map.get("Alice"); // Some(&30)💡 Use v.get(i) instead of v[i] to avoid panics — returns Option<&T>
⚡ The entry().or_insert() pattern is the idiomatic way to insert-if-absent in HashMaps
📌 .collect() can build Vec, HashMap, String, and more — the target type determines behavior
🟢 Use &v to borrow during iteration, v to consume, &mut v to mutate in place
vechashmapcollections