rustType errorMedium

Downcast on Box dyn Any fails with wrong type

Time: 0:00

BugFind the bug and fix the code

What it should do

Downcast Any to i32, or return -1 if type mismatch. Example: downcast_any_value(true) -> 42

What happens instead

panicked at 'called `Option::unwrap()` on a `None` value' during downcast

use std::any::Any;

fn downcast_any_value(is_int: bool) -> i32 {
    let boxed: Box<dyn Any> = if is_int {
        Box::new(42_i32)
    } else {
        Box::new("hello".to_string())
    };
    // .downcast::<i32>().unwrap() panics if boxed is String
    *boxed.downcast::<i32>().unwrap()
}

fn main() {
    println!("{}", downcast_any_value(true));
}

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 type errors pattern

Totals that concatenate, sorts that put 10 before 9, comparisons that refuse to run.

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use std::any::Any; fn downcast_any_value(is_int: bool) -> i32 { let boxed: Box<dyn Any> = if is_int { Box::new(42_i32) } else { Box::new("hello".to_string()) }; // .downcast::<i32>().unwrap() panics if boxed is String *boxed.downcast::<i32>().unwrap() } fn main() { println!("{}", downcast_any_value(true)); }

Downcast on Box dyn Any fails with wrong type

What it should do

What happens instead

More type errors to practise

Downcast on Box dyn Any fails with wrong type

What it should do

What happens instead

More type errors to practise