try_into_opt!

Overview

Like try!, but turns a Result into an Option, mainly for use in a filter_map. Provides early return for errors like try! does in map.

try_into_opt! is different from try_opt!, which provides early return for functions that return an Option. try_into_opt operates on functions that return a Result but your code requires an option. This scenario may come up when doing IO that can fail, but if it succeeds, needs to be filtered in some way.

Usage

Add this to your Cargo.toml:

[dependencies]
try_into_opt = "0.1.0"

And to your crate:

#[macro_use]
extern crate try_into_opt;

Example

#[macro_use]
extern crate try_into_opt;

const MAX_NUM: usize = 11usize;

fn num_range_filter(v: &[usize]) -> Result<Vec<usize>, String> {
    v.iter()
     .filter_map(|i| {
         let i = try_into_opt!(validate_num(*i));

         // do some filtering...
         if i == 5 {
             None
         } else {
             Some(Ok(i))
         }
     })
     .collect()
}

fn validate_num(i: usize) -> Result<usize, String> {
    if i > MAX_NUM {
        Err(format!("{} is larger than the allowed max of {}", i, MAX_NUM))
    } else {
        Ok(i)
    }
}

fn main() {
    let nums = num_range_filter(&[1, 2, 3, 10, 12, 0]);
    assert_eq!(nums.is_err(), true);

    let nums = num_range_filter(&[1, 2, 5, 3, 5, 10, 0, 5]).unwrap();
    assert_eq!(nums, [1, 2, 3, 10, 0]);
}

For more details, head over to the documentation.

License

This library is distributed under similar terms to Rust: dual-licensed under the MIT license and the Apache license (version 2.0).

See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.