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// 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))
        }
    })
}