Rust: What is the difference between Vec and array?

Vec — dynamic, heap-allocated, growable. Array — fixed-size, stack-allocated, Copy.

Vec:

• Dynamically sized at runtime.
• Heap allocated — pointer, length, capacity.
• Can grow or shrink with .push(), .pop().
• Cannot implement Copy (owns heap data).
• Rich API for manipulation.

1let mut v = vec![1, 2, 3];
2v.push(4);
3v.pop();
4v.insert(0, 0);
5println!("{:?}", v);  // [0, 1, 2]

Array:

• Fixed size, compile-time known.
• Stack allocated — fast, no heap overhead.
• Implements Copy if elements do.
• Cannot grow or shrink.
• Useful for fixed-size data.

1let a: [i32; 3] = [1, 2, 3];
2let zeros = [0; 5];
3let first = a[0];  // 1
4let len = a.len(); // 3

When to use:

• Use Vec for most collection needs.
• Use arrays for small, fixed-size data.
• Use slices to abstract over both.

Common mistakes:

• Trying to push to an array — not allowed.
• Confusing vec! return type with arrays.
• Not converting Vec to slice when needed.