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 1.34+
Result<T, anyhow::Error>, or equivalently
anyhow::Result<T>, as the return type of any fallible function.
Within the function, use
?to easily propagate any error that implements the
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.
Error: Failed to read instrs from ./path/to/instrs.json 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=1environment 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 a
derive(Error)macro but you can write the impls yourself or use a standalone macro like thiserror.
One-off error messages can be constructed using the
anyhow!macro, which supports string interpolation and produces an
Comparison to failure
anyhow::Error type works something like
failure::Error, but unlike
failure ours is built around the standard library's
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.
Comparison to thiserror
Use Anyhow if you don't care what error type your functions return, you just want it to be easy. This is common in application code. Use thiserror if you are a library that wants to design your own dedicated error type(s) so that on failures the caller gets exactly the information that you choose.