Rust: What is the difference between Ref and RefMut?

Ref — immutable borrow. RefMut — mutable borrow.

Ref:

• Multiple immutable borrows.
• Cannot modify.
• Read-only access.

RefMut:

• Exclusive mutable borrow.
• Can modify.
• Read-write access.

1use std::cell::RefCell;
2
3let data = RefCell::new(vec![1, 2, 3]);
4
5{
6    let borrow = data.borrow();
7    println!("{:?}", *borrow);
8}
9
10{
11    let mut borrow = data.borrow_mut();
12    borrow.push(4);
13}

Key: Ref for reading, RefMut for writing.