Anyhow ¯\_(ツ)_/¯
This library provides anyhow::Error
, a trait object based error type
for easy idiomatic error handling in Rust applications.
[]
= "1.0"
Compiler support: requires rustc 1.32+
Details
-
Use
Result<T, anyhow::Error>
, or equivalentlyanyhow::Result<T>
, as the return type of any fallible function.Within the function, use
?
to easily propagate any error that implements thestd::error::Error
trait.use Result;
-
Attach context to help the person troubleshooting the error understand where things went wrong. A low-level error like "No such file or directory" can be annoying to debug without more context about what higher level step the application was in the middle of.
use ;
Error: failed to read instrs from ./path/to/instrs.jsox Caused by: No such file or directory (os error 2)
-
Downcasting is supported and can be by value, by shared reference, or by mutable reference as needed.
// If the error was caused by redaction, then return a // tombstone instead of the content. match root_cause.
-
A backtrace is captured and printed with the error if the underlying error type does not already provide its own. In order to see backtraces, the
RUST_LIB_BACKTRACE=1
environment variable must be defined. -
Anyhow works with any error type that has an impl of
std::error::Error
, including ones defined in your crate. We do not bundle aderive(Error)
macro but you can write the impls yourself or use a standalone macro like err-derive. -
One-off error messages can be constructed using the
anyhow!
macro, which supports string interpolation and produces ananyhow::Error
.return Err;
Comparison to failure
The anyhow::Error
type works something like failure::Error
, but unlike
failure ours is built around the standard library's std::error::Error
trait
rather than a separate trait failure::Fail
. The standard library has adopted
the necessary improvements for this to be possible as part of RFC 2504.
Acknowledgements
The implementation of the anyhow::Error
type is forked from
fehler::Exception
(https://github.com/withoutboats/fehler). This library just
exposes it under the more standard Error
/ Result
terminology rather than
the throw!
/ #[throws]
/ Exception
language of exceptions.