Compiler Borrow Checker Constraints

Rust compiler borrow checker

Compiler borrow checker constraints

The Rust program below gives the compiler errors. Look at the main function and try to understand the errors and suggest a possible fix.

Code

 fn main() {     let mut d1 = Dictionary.new();     d1.add_word("hello");     d1.add_word("world!"); }  struct Dictionary {     data: Vec<String>, }  impl Dictionary {     fn new() -> Self {         Dictionary { data: Vec::new() }     }      fn add_word(&mut self, word: &str) {         self.data.push(word.to_string());     } }  

Error messages

• Cannot borrow self as mutable more than once at a time -- src/main.rs:46:29
• for order_id in mut self.map_order_id_position -----
• The only way this is possible except for unsafe code is that the resulting reference is somehow derived from the incoming reference (for example, it references some field inside the object).
• The add_word method gives these 5 errors
• Cannot borrow cursor as mutable more than once at a time.
• Since Rust no longer supports immutable struct fields and apparently since the borrow checker does not perform interprocedural analysis, the compiler acts as if one of the mut.
• In practice, this means Rust's borrow checker will only allow at most one call to some_method before the struct becomes permanently mutably borrowed and thus unusable.

Conclusion

The Rust compiler borrow checker is a powerful tool that helps to ensure the memory safety of Rust programs. However, it can sometimes be difficult to understand the errors that the borrow checker generates. In this case, the error is due to the fact that the add_word method borrows the self parameter mutably. This means that the self parameter cannot be borrowed again until the add_word method returns. The fix is to move the add_word method to the Dictionary struct. This will allow the add_word method to borrow the self parameter mutably without violating the borrow checker's rules.