This library provides anyhow::Error, a trait object based error type
for easy idiomatic error handling in Rust applications.
toml
[dependencies]
anyhow = "1.0"
Compiler support: requires rustc 1.34+
Use 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
std::error::Error trait.
```rust use anyhow::Result;
fn getclusterinfo() -> 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.
```rust use anyhow::{Context, Result};
fn main() -> Result<()> { ... it.detach().context("Failed to detach the important thing")?;
let content = std::fs::read(path) .with_context(|| format!("Failed to read instrs from {}", path))?; ... } ```
```console 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.
rust
// If the error was caused by redaction, then return a
// tombstone instead of the content.
match root_cause.downcast_ref::<DataStoreError>() {
Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)),
None => Err(error),
}
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 a derive(Error) macro
but you can write the impls yourself or use a standalone macro like
[thiserror].
```rust use thiserror::Error;
pub enum FormatError { #[error("Invalid header (expected {expected:?}, got {found:?})")] InvalidHeader { expected: String, found: String, }, #[error("Missing attribute: {0}")] MissingAttribute(String), } ```
One-off error messages can be constructed using the anyhow! macro, which
supports string interpolation and produces an anyhow::Error.
rust
return Err(anyhow!("Missing attribute: {}", missing));
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].
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.
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.