std::try!

macro_rules! try {
    ($expr:expr) => (match $expr {
        $crate::result::Result::Ok(val) => val,
        $crate::result::Result::Err(err) => {
            return $crate::result::Result::Err($crate::convert::From::from(err))
        }
    })
}

Helper macro for unwrapping Result values while returning early with an error if the value of the expression is Err. Can only be used in functions that return Result because of the early return of Err that it provides.

Examples

fn main() { use std::io; use std::fs::File; use std::io::prelude::*; fn write_to_file_using_try() -> Result<(), io::Error> { let mut file = try!(File::create("my_best_friends.txt")); try!(file.write_all(b"This is a list of my best friends.")); println!("I wrote to the file"); Ok(()) } // This is equivalent to: fn write_to_file_using_match() -> Result<(), io::Error> { let mut file = try!(File::create("my_best_friends.txt")); match file.write_all(b"This is a list of my best friends.") { Ok(_) => (), Err(e) => return Err(e), } println!("I wrote to the file"); Ok(()) } }

use std::io;
use std::fs::File;
use std::io::prelude::*;

fn write_to_file_using_try() -> Result<(), io::Error> {
    let mut file = try!(File::create("my_best_friends.txt"));
    try!(file.write_all(b"This is a list of my best friends."));
    println!("I wrote to the file");
    Ok(())
}
// This is equivalent to:
fn write_to_file_using_match() -> Result<(), io::Error> {
    let mut file = try!(File::create("my_best_friends.txt"));
    match file.write_all(b"This is a list of my best friends.") {
        Ok(_) => (),
        Err(e) => return Err(e),
    }
    println!("I wrote to the file");
    Ok(())
}