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use core::fmt::{self, Display, Debug};

use Fail;
use Error;

/// Constructs a `Fail` type from a string.
///
/// This is a convenient way to turn a string into an error value that
/// can be passed around, if you do not want to create a new `Fail` type for
/// this use case.
pub fn err_msg<D: Display + Debug + Sync + Send + 'static>(msg: D) -> Error {
    Error::from(ErrorMessage { msg })
}

/// A `Fail` type that just contains an error message. You can construct
/// this from the `err_msg` function.
#[derive(Debug)]
struct ErrorMessage<D: Display + Debug + Sync + Send + 'static> {
    msg: D,
}

impl<D: Display + Debug + Sync + Send + 'static> Fail for ErrorMessage<D> { }

impl<D: Display + Debug + Sync + Send + 'static> Display for ErrorMessage<D> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Display::fmt(&self.msg, f)
    }
}

/// Constructs an `Error` using the standard string interpolation syntax.
///
/// ```rust
/// #[macro_use] extern crate failure;
///
/// fn main() {
///     let code = 101;
///     let err = format_err!("Error code: {}", code);
/// }
/// ```
#[macro_export]
macro_rules! format_err {
    ($($arg:tt)*) => { $crate::err_msg(format!($($arg)*)) }
}