about the borrowing example

[trichimtrich]

Hi, I'm new to Rust and trying the sample in this doc https://learning-rust.github.io/docs/borrowing/

The code

fn main() {
  let mut a = vec![1, 2, 3];
  let b = &mut a;  //  &mut borrow of `a` starts here
  // some code
b[1] = 123;

  println!("{:?}", a); // trying to access `a` as a shared borrow, so giving an error
}                  //  &mut borrow of `a` ends here

It seems to compile and run fine without any error on my machine

ubt :: testbin ‹master› % rustc --version                      1 ↵
rustc 1.78.0 (9b00956e5 2024-04-29)
ubt :: testbin ‹master› % cargo run
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s
     Running `target/debug/testbin`
[1, 123, 3]

Is it intended, or something has changed from the language itself.

[c4p1t4n]

i'm new in rust too, i compiled this code and received the same result that u. I know that the language is retro-compatibility. In my mind that is just a mistake in documentation. I think that the correct code to get an error is

fn main() {
  let mut a = vec![1, 2, 3];
  let b = a;  //  &mut borrow of `a` starts here
  // some code
    b[1] = 123;

  println!("{:?}", a); // trying to access `a` as a shared borrow, so giving an error
}          

In this case the ownership of a is moved to b, and you can't access a in the print line

[dumindu]

@trichimtrich Thanks for highlighting this. In 2018-2022, Rust ecosystem added more improvements for lifetimes, especially to improve DX; https://users.rust-lang.org/t/multiple-mutable-references-in-scope/20936 but the given code block was written in 2017. I think I need to double check NLLs in the examples of those sections and update them.