Release 1.0.0
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  5. LICENSE-MIT
  6. README.md
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  9. tests/
README.md

derive(Error)

Build Status Latest Version Rust Documentation

This library provides a convenient derive macro for the standard library's std::error::Error trait.

[dependencies]
thiserror = "1.0"

Compiler support: requires rustc 1.31+

Example

use thiserror::Error;

#[derive(Error, Debug)]
pub enum DataStoreError {
    #[error("data store disconnected")]
    Disconnect(#[source] io::Error),
    #[error("the data for key `{0}` is not available")]
    Redaction(String),
    #[error("invalid header (expected {expected:?}, found {found:?})")]
    InvalidHeader {
        expected: String,
        found: String,
    },
    #[error("unknown data store error")]
    Unknown,
}

Details

  • Errors may be enums, structs with named fields, tuple structs, or unit structs.

  • A Display impl is generated for your error if you provide #[error("...")] messages on the struct or each variant of your enum, as shown above in the example.

    The messages support a shorthand for interpolating fields from the error.

    • #[error("{var}")]write!("{}", self.var)
    • #[error("{0}")]write!("{}", self.0)
    • #[error("{var:?}")]write!("{:?}", self.var)
    • #[error("{0:?}")]write!("{:?}", self.0)

    You may alternatively write out the full format args yourself, using arbitrary expressions.

    When providing your own format args, the shorthand does not kick in so you need to specify .var in the argument list to refer to named fields and .0 to refer to tuple fields.

    #[derive(Error, Debug)]
    pub enum Error {
        #[error("invalid rdo_lookahead_frames {} (expected < {})", .0, i32::max_value())]
        InvalidLookahead(i32),
    }
    
  • The Error trait's source() method is implemented to return whichever field has a #[source] attribute, if any. This is for identifying the underlying lower level error that caused your error.

    Any error type that implements std::error::Error or dereferences to dyn std::error::Error will work as a source.

    #[derive(Error, Debug)]
    pub struct MyError {
        msg: String,
        #[source]
        source: anyhow::Error,
    }
    
  • The Error trait's backtrace() method is implemented to return whichever field has a type named Backtrace, if any.

    use std::backtrace::Backtrace;
    
    #[derive(Error, Debug)]
    pub struct MyError {
        msg: String,
        backtrace: Backtrace, // automatically detected
    }
    
  • See also the anyhow library for a convenient single error type to use in application code.

License