1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76
// Copyright 2010-2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. /*! A useful crate to avoid any possible deprecation warnings of the try macro. Since the introduction of the `?` operator, its supporters have preffered its use, ignoring the valid criticism of the `?` operator almost hiding the error propagation operation. The `try!` operator is far more visible and thus doesn't hide the functionality, allowing for more readable code. */ /// Helper macro for reducing boilerplate code for matching `Result` together /// with converting downstream errors. /// /// `try!` matches the given `Result`. In case of the `Ok` variant, the /// expression has the value of the wrapped value. /// /// In case of the `Err` variant, it retrieves the inner error. `try!` then /// performs conversion using `From`. This provides automatic conversion /// between specialized errors and more general ones. The resulting /// error is then immediately returned. /// /// Because of the early return, `try!` can only be used in functions that /// return `Result`. /// /// # Examples /// /// ``` /// use std::io; /// use std::fs::File; /// use std::io::prelude::*; /// /// enum MyError { /// FileWriteError /// } /// /// impl From<io::Error> for MyError { /// fn from(e: io::Error) -> MyError { /// MyError::FileWriteError /// } /// } /// /// fn write_to_file_using_try() -> Result<(), MyError> { /// 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<(), MyError> { /// let mut file = try!(File::create("my_best_friends.txt")); /// match file.write_all(b"This is a list of my best friends.") { /// Ok(v) => v, /// Err(e) => return Err(From::from(e)), /// } /// println!("I wrote to the file"); /// Ok(()) /// } /// ``` #[macro_export] macro_rules! try { ($expr:expr) => (match $expr { Ok(val) => val, Err(err) => { return Err(std::convert::From::from(err)) } }) }