rust borrow_error ai_generated true

cannot borrow `*self` as mutable because it is also borrowed as immutable

ID: rust/rust-cannot-borrow-mut

Also available as: JSON · Markdown
87%Fix Rate
90%Confidence
50Evidence
2023-01-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1 active — — —

Root Cause

Simultaneous mutable and immutable borrows violate Rust's aliasing rules. Restructure code to separate borrow scopes.

generic

Workarounds

  1. 90% success Extract the immutable read into a local variable before the mutable borrow 
    let value = self.field.clone();
self.other_field = transform(value);

    Sources: https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html

  2. 85% success Use interior mutability with Cell or RefCell 
    use std::cell::RefCell;
let field = RefCell::new(value);
// Now you can borrow_mut() independently

    Sources: https://doc.rust-lang.org/std/cell/index.html

Dead Ends

Common approaches that don't work:

  1. Use unsafe block to force mutable access while immutable reference exists 95% fail

    Undefined behavior; the compiler relies on aliasing guarantees for optimization

  2. Clone the entire struct to avoid borrow conflicts 60% fail

    Excessive memory usage and doesn't fix the underlying design issue; changes may be lost

Error Chain

Leads to:
Preceded by:
Frequently confused with: