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#![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png", html_favicon_url = "https://www.rust-lang.org/favicon.ico", html_root_url = "https://wisagan.github.io/simple-error/simple_error/")] #![deny(missing_docs)] //! A simple error type backed by a string. //! //! This crate provides a `SimpleError` type, which implements `std::error::Error`. The underlying //! is a `String` as the error message. //! //! It should be used when all you care about is an error string. //! //! It should not be used when you want to programmatically handle different kinds of an error. use std::fmt; /// A type that represents a simple error. /// /// This type uses a `String` to store the error string, and it implements `std::error::Error`. #[derive(Clone, Debug, PartialEq, Eq)] pub struct SimpleError { err: String, } impl SimpleError { /// Creates a new simple error. /// /// This function can take any type that implements `Into<String>`. /// /// # Examples /// /// ``` /// use self::simple_error::SimpleError; /// /// // errors can be created from `str` /// let err = SimpleError::new("an error from str"); /// /// // errors can also be created from `String` /// let err = SimpleError::new(String::from("an error from String")); /// ``` #[inline] pub fn new<T: Into<String>>(t: T) -> SimpleError { SimpleError{ err: t.into() } } /// Creates a new simple error from another error. /// /// This function can take any type that implements `std::error::Error`. /// The error string will be the `Display` of the `std::error::Error`. /// /// # Examples /// /// ``` /// use self::simple_error::SimpleError; /// use std::io; /// /// // errors can be created from `io::Error` /// let err = SimpleError::from(io::Error::new(io::ErrorKind::Other, "oh no")); /// assert_eq!("oh no", format!("{}", err)); /// ``` #[inline] pub fn from<T: std::error::Error>(t: T) -> SimpleError { SimpleError{ err: format!("{}", t) } } /// Creates a new simple error from a string with another error. /// /// This function takes a string as error and a type that implements `std::error::Error` as /// reason. /// The error string will be the `Display` of the `std::error::Error` prefixed with the string /// and ", ". /// /// # Examples /// /// ``` /// use self::simple_error::SimpleError; /// /// let err = SimpleError::with("cannot turn on tv", SimpleError::new("remote not found")); /// assert_eq!("cannot turn on tv, remote not found", format!("{}", err)); /// ``` #[inline] pub fn with<T: std::error::Error>(s: &str, t: T) -> SimpleError { SimpleError{ err: format!("{}, {}", s, t) } } } // TODO: implement From<T> where T: std::error::Error when specialization lands, and remove // inherent from function. impl fmt::Display for SimpleError { #[inline] fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { self.err.fmt(f) } } impl std::error::Error for SimpleError { #[inline] fn description(&self) -> &str { &self.err } } /// Helper macro for unwrapping `Result` values while returning early with a /// newly constructed `SimpleError` if the value of the expression is `Err`. /// Can only be used in functions that return `Result<_, SimpleError>`. /// /// /// # Examples /// /// ``` /// # #[macro_use] extern crate simple_error; /// # fn main() { /// use self::simple_error::SimpleError; /// /// fn try_block(result: Result<(), SimpleError>, s: &str) -> Result<(), SimpleError> { /// Ok(try_with!(result, s)) /// } /// /// // Above is equivalent to below. /// /// fn try_block_equivalent(result: Result<(), SimpleError>, s: &str) -> Result<(), SimpleError> { /// match result { /// Ok(v) => Ok(v), /// Err(e) => { /// return Err(SimpleError::with(s, e)); /// }, /// } /// } /// # } /// ``` #[macro_export] macro_rules! try_with { ($expr: expr, $str: expr) => (match $expr { Ok(val) => val, Err(err) => { return Err(SimpleError::with($str, err)); }, }) } #[cfg(test)] mod tests { use super::SimpleError; use std::error::Error; use std::io; #[test] fn new_from_string() { let err = SimpleError::new(String::from("an error from String")); assert_eq!("an error from String", format!("{}", err)); assert_eq!("an error from String", err.description()); } #[test] fn new_from_str() { let err = SimpleError::new("an error from str"); assert_eq!("an error from str", format!("{}", err)); } #[test] fn from_io_error() { let err = SimpleError::from(io::Error::new(io::ErrorKind::Other, "oh no")); assert_eq!("oh no", format!("{}", err)); } fn try_block(result: Result<(), SimpleError>, s: &str) -> Result<(), SimpleError> { Ok(try_with!(result, s)) } #[test] fn macro_try_with() { assert_eq!(Ok(()), try_block(Ok(()), "")); assert_eq!(Err(SimpleError::new("try block error, error foo")), try_block(Err(SimpleError::new("error foo")), "try block error")); } }