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#![no_std]

#[cfg(feature = "std")]
extern crate std;

use core::fmt::*;

#[cfg(feature = "std")]
pub use std::error::Error;

#[cfg(not(feature = "std"))]
pub trait Error: Debug + Display {
    /// A short description of the error.
    ///
    /// The description should only be used for a simple message.
    /// It should not contain newlines or sentence-ending punctuation,
    /// to facilitate embedding in larger user-facing strings.
    /// For showing formatted error messages with more information see
    /// [`Display`].
    ///
    /// [`Display`]: ../fmt/trait.Display.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::error::Error;
    ///
    /// match "xc".parse::<u32>() {
    ///     Err(e) => {
    ///         println!("Error: {}", e.description());
    ///     }
    ///     _ => println!("No error"),
    /// }
    /// ```
    fn description(&self) -> &str;

    /// The lower-level cause of this error, if any.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::error::Error;
    /// use std::fmt;
    ///
    /// #[derive(Debug)]
    /// struct SuperError {
    ///     side: SuperErrorSideKick,
    /// }
    ///
    /// impl fmt::Display for SuperError {
    ///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    ///         write!(f, "SuperError is here!")
    ///     }
    /// }
    ///
    /// impl Error for SuperError {
    ///     fn description(&self) -> &str {
    ///         "I'm the superhero of errors"
    ///     }
    ///
    ///     fn cause(&self) -> Option<&Error> {
    ///         Some(&self.side)
    ///     }
    /// }
    ///
    /// #[derive(Debug)]
    /// struct SuperErrorSideKick;
    ///
    /// impl fmt::Display for SuperErrorSideKick {
    ///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    ///         write!(f, "SuperErrorSideKick is here!")
    ///     }
    /// }
    ///
    /// impl Error for SuperErrorSideKick {
    ///     fn description(&self) -> &str {
    ///         "I'm SuperError side kick"
    ///     }
    /// }
    ///
    /// fn get_super_error() -> Result<(), SuperError> {
    ///     Err(SuperError { side: SuperErrorSideKick })
    /// }
    ///
    /// fn main() {
    ///     match get_super_error() {
    ///         Err(e) => {
    ///             println!("Error: {}", e.description());
    ///             println!("Caused by: {}", e.cause().unwrap());
    ///         }
    ///         _ => println!("No error"),
    ///     }
    /// }
    /// ```
    fn cause(&self) -> Option<&Error> { None }
}