[−][src]Crate anyhow
+
This library provides anyhow::Error, a trait object based error
+type for easy idiomatic error handling in Rust applications.
+
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::Errortrait.++use anyhow::Result; + +fn get_cluster_info() -> Result<ClusterMap> { + let config = std::fs::read_to_string("cluster.json")?; + let map: ClusterMap = serde_json::from_str(&config)?; + Ok(map) +}
+ -
+
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 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))?; + ... +}
+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.downcast_ref::<DataStoreError>() { + Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)), + None => Err(error), +}
+ -
+
If using the nightly channel, 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, they must be enabled through the environment +variables described in
+std::backtrace:-
+
- If you want panics and errors to both have backtraces, set
+
RUST_BACKTRACE=1;
+ - If you want only errors to have backtraces, set
RUST_LIB_BACKTRACE=1;
+ - If you want only panics to have backtraces, set
RUST_BACKTRACE=1and +RUST_LIB_BACKTRACE=0.
+
The tracking issue for this feature is rust-lang/rust#53487.
+
+ - If you want panics and errors to both have backtraces, set
+
-
+
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 +thiserror.++use thiserror::Error; + +#[derive(Error, Debug)] +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 ananyhow::Error.++return Err(anyhow!("Missing attribute: {}", missing));
+
+
No-std support
+In no_std mode, the same API is almost all available and works the same way. +To depend on Anyhow in no_std mode, disable our default enabled "std" +feature in Cargo.toml. A global allocator is required.
+[dependencies]
+anyhow = { version = "1.0", default-features = false }
+Since the ?-based error conversions would normally rely on the
+std::error::Error trait which is only available through std, no_std mode
+will require an explicit .map_err(Error::msg) when working with a
+non-Anyhow error type inside a function that returns Anyhow's error type.
Re-exports
+pub use anyhow as format_err; |
Macros
+| anyhow | Construct an ad-hoc error from a string. + |
| bail | Return early with an error. + |
| ensure | Return early with an error if a condition is not satisfied. + |
Structs
+| Chain | Iterator of a chain of source errors. + |
| Error | The |
Traits
+| Context | Provides the |
Type Definitions
+| Result |
|