Macro unwrap_ok

macro_rules! unwrap_ok {
    ($res:expr) => { ... };
}

Gets the value in the Ok variant.

Panics

This panics if $res is an Err, including the debug-formatted error in the panic message.

Example

The struct formatting below requires the "non_basic" feature (enabled by default)

use const_panic::unwrap_ok;

const SUM: u64 = unwrap_ok!(add_up_evens(&[2, 4, 8, 16]));

assert_eq!(SUM, 30);

const fn add_up_evens(slice: &[u8]) -> Result<u64, OddError> {
    let mut sum = 0u64;
    let mut i = 0;

    while i < slice.len() {
        let x = slice[i];

        if x % 2 == 1 {
            return Err(OddError{at: i, number: x});
        }

        sum += x as u64;
        i += 1;
    }
     
    Ok(sum)
}


struct OddError {
    at: usize,
    number: u8,
}

// You can also use `#[derive(PanicFmt))]` with the "derive" feature
const_panic::impl_panicfmt!{
    struct OddError {
        at: usize,
        number: u8,
    }
}

Error

This is what the compile-time error looks like when attempting to unwrap an Err:

error[E0080]: evaluation of constant value failed
 --> src/macros/unwrapping.rs:51:18
  |
6 | const SUM: u64 = unwrap_ok!(add_up_evens(&[3, 5, 8, 13]));
  |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at '
invoked `unwrap_ok` macro with an `Err` value: OddError { at: 0, number: 3 }', src/macros/unwrapping.rs:6:18
  |