I am implementing an in-place recursive parser in rust and I am getting some borrow errors. The code snippet reproduces the problem although it is not very useful
use std::vec::Vec; struct MyBorrows<'a> { val : &'a mut i32 } impl <'a> MyBorrows<'a> { fn new(v : &'a mut i32) -> MyBorrows<'a> { MyBorrows { val : v } } } fn main() { let mut my_val = 23; let mut my_vec : Vec<Box<MyBorrows>> = Vec::new(); my_vec.push(Box::new(MyBorrows::new(&mut my_val))); for i in [1..4].iter() { let mut last : &mut Box<MyBorrows> = my_vec.last_mut().unwrap(); let mut new_borrow = Box::new(MyBorrows::new(last.val)); my_vec.push(new_borrow); } } This gives me the following error:
error[E0499]: cannot borrow `my_vec` as mutable more than once at a time --> test.rs:20:9 | 18 | let mut last : &mut Box = my_vec.last_mut().unwrap(); | ------ first mutable borrow occurs here 19 | let mut new_borrow = Box::new(MyBorrows::new(last.val)); 20 | my_vec.push(new_borrow); | ^^^^^^ second mutable borrow occurs here 21 | } 22 | } | - first borrow ends here error: aborting due to 3 previous errors
In my real case, the vector is used as a stack to reference deeper and deeper components of the struct I am parsing into. This is common pattern I use for general purpose parsing in C++ which I am trying to replicate in Rust but I am having problems. Any help will be appreciated.
