This library provides a convenient derive macro for the standard library's
[std::error::Error] trait.
toml
[dependencies]
thiserror = "1.0"
Compiler support: requires rustc 1.31+
```rust use thiserror::Error;
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,
}
```
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.
```rust
pub enum Error { #[error("invalid rdolookaheadframes {} (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.
```rust
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.
```rust use std::backtrace::Backtrace;
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.
Licensed under either of Apache License, Version 2.0 or MIT license at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.