prog.rs:4:5: 4:6 error: cannot borrow `a` as mutable because it is also borrowed as immutable
prog.rs:4 a.push(1);
^
prog.rs:3:14: 3:15 note: previous borrow of `a` occurs here; the immutable borrow prevents subsequent moves or mutable borrows of `a` until the borrow ends
prog.rs:3 let b = &a;
^
prog.rs:5:2: 5:2 note: previous borrow ends here
prog.rs:1 fn main() {
prog.rs:2 let mut a = Vec::new();
prog.rs:3 let b = &a;
prog.rs:4 a.push(1);
prog.rs:5 }
^
error: aborting due to previous error