rustScope errorMedium

Borrow checker vector mutation during element iteration

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What it should do

Filter and collect even numbers from list. Example: duplicate_even_numbers([1, 2, 3, 4]) -> [2, 4]

What happens instead

Compiler error: cannot borrow vec as mutable because it is also borrowed as immutable

fn duplicate_even_numbers(nums: Vec<i32>) -> Vec<i32> {
    let mut result = nums.clone();
    for n in &nums {
        if n % 2 != 0 {
            // Cannot modify result while iterating or wrong filter
        }
    }
    nums.into_iter().filter(|x| x % 2 == 0).collect()
}

fn main() {
    println!("{:?}", duplicate_even_numbers(vec![1, 2, 3, 4]));
}

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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fn duplicate_even_numbers(nums: Vec<i32>) -> Vec<i32> { let mut result = nums.clone(); for n in &nums { if n % 2 != 0 { // Cannot modify result while iterating or wrong filter } } nums.into_iter().filter(|x| x % 2 == 0).collect() } fn main() { println!("{:?}", duplicate_even_numbers(vec![1, 2, 3, 4])); }

Borrow checker vector mutation during element iteration

What it should do

What happens instead

More scope and closure bugs to practise

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Borrow checker vector mutation during element iteration

What it should do

What happens instead

More scope and closure bugs to practise

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