anyhow

anyhow provides anyhow::Result<T> and context attachments for application binaries where error taxonomy is not part of the public API.

Recipe

[dependencies]
anyhow = "1"

use anyhow::{Context, Result};
 
fn read_port(path: &str) -> Result<u16> {
    let s = std::fs::read_to_string(path)
        .with_context(|| format!("reading {path}"))?;
    let port: u16 = s.trim().parse().context("parsing port")?;
    Ok(port)
}

When to reach for this: CLIs, servers, and binaries - not published library error types.

Working Example

fn main() -> anyhow::Result<()> {
    let port = read_port("PORT")?;
    println!("port={port}");
    Ok(())
}

What this demonstrates:

• main returns anyhow::Result
• ? propagates with context chain
• Single error type erases specifics at boundary

Deep Dive

anyhow::Error is Send + Sync + 'static, supports downcasting in tests via downcast_ref.

Gotchas

• anyhow in library public API - Consumers cannot match errors. Fix: thiserror enum.
• Relying on Display text in tests - Fragile. Fix: Downcast or structured tests at boundary.
• Context closure allocation - with_context(|| ...) lazy. Fix: Use context for static strings.
• Mixing anyhow and custom errors - Use ? with From or .map_err(Into::into).
• No backtrace by default - Enable RUST_BACKTRACE + anyhow feature flags.

Alternatives

FAQs

Related

• thiserror
• Error Context & Backtraces
• The ? Operator
• clap Error Reporting

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.