Rust: What is the difference between Vec and array?

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

Vec:

• Dynamically sized at runtime (grows/shrinks).
• Heap allocated — pointer, length, capacity.
• Cannot implement Copy (heap data).
• Rich API: .push(), .pop(), .insert(), .remove().
• Slightly slower due to heap indirection.

1let mut v = vec![1, 2, 3];
2v.push(4);       // Grows
3v.pop();         // Shrinks
4println!("{:?}", v);  // [1, 2]
5let v2 = vec![0; 10]; // [0; 10] zeros

Array:

• Fixed size, known at compile time ([T; N]).
• Stack allocated — fast, no heap overhead.
• Implements Copy if elements do.
• No grow/shrink methods — size is immutable.
• Bounds checked at runtime.

1let a: [i32; 3] = [1, 2, 3];
2let zeros = [0; 5];  // [0, 0, 0, 0, 0]
3let first = a[0];   // 1

When to use:

• Use Vec for most collection needs (default choice).
• Use arrays for small, fixed-size data (coordinates, RGB, buffers).
• Use slices (&[T]) to abstract over both.

Common mistakes:

• Trying to push to an array — not possible.
• Not realizing vec! returns Vec, not [T; N].
• Using arrays when size might change — use Vec.