rustScope errorMedium

Panic on accessing nested RefCell data

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BugFind the bug and fix the code

What it should do

Example: process_refcell_data(data) -> processed data

What happens instead

thread 'main' panicked at 'AlreadyBorrowed: RefCell is already borrowed'

use std::cell::RefCell; 

fn process_refcell_data(data: &RefCell<Vec<RefCell<i32>>>) -> i32 {
    let outer_ref = data.borrow();
    let inner_ref = outer_ref[0].borrow();
    *inner_ref + 1
}

fn main() {
    let data = RefCell::new(vec![RefCell::new(5)]);
    println!("Processed: {}", process_refcell_data(&data));
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the scope and closure bugs pattern

Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.

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use std::cell::RefCell; fn process_refcell_data(data: &RefCell<Vec<RefCell<i32>>>) -> i32 { let outer_ref = data.borrow(); let inner_ref = outer_ref[0].borrow(); *inner_ref + 1 } fn main() { let data = RefCell::new(vec![RefCell::new(5)]); println!("Processed: {}", process_refcell_data(&data)); }

Panic on accessing nested RefCell data

What it should do

What happens instead

More scope and closure bugs to practise

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Panic on accessing nested RefCell data

What it should do

What happens instead

More scope and closure bugs to practise

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