#log #logging #slog


Extension traits for logging failed unwraps to a slog::Logger

10 releases

0.9.2 Aug 27, 2020
0.9.1 Apr 8, 2020
0.8.0 Apr 8, 2020
0.1.5 Apr 5, 2020

#205 in Debugging

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This crate provides .unwrap_or_log() and .expect_or_log() methods on Result and Option types that log failed unwraps to a slog::Logger. This is useful when, for example, you have a syslog drain or a database drain, and you want your unwrap failures to show up there instead of being printed to stderr.

Its API aims to mirror Rust's std — see all the supported methods below. Failed unwraps are logged at a level of Critical.

crates.io Documentation License


Add the following to your Cargo.toml:

slog-unwrap = "0.9"

Next, bring the ResultExt and/or OptionExt traits into scope, and make use of the new logging methods.

use slog_unwrap::ResultExt;

let logger = slog::Logger::root(slog::Discard, slog::o!());
let not_great: Result<(), _> = Result::Err("not terrible");

// Logs the failed unwrap to `logger` and panics


std method slog-unwrap form trait
Result::unwrap() Result::unwrap_or_log(&log) ResultExt
Result::expect(msg) Result::expect_or_log(&log, msg) ResultExt
Result::unwrap_err() Result::unwrap_err_or_log(&log) ResultExt
Result::expect_err(msg) Result::expect_err_or_log(&log, msg) ResultExt
Option::unwrap() Option::unwrap_or_log(&log) OptionExt
Option::expect(msg) Option::expect_or_log(&log, msg) OptionExt
Option::unwrap_none() Option::unwrap_none_or_log(&log) OptionExt
Option::expect_none(msg) Option::expect_none_or_log(&log, msg) OptionExt

†: unstable in std
Note: enabling the scope feature drops the &log argument from all methods.


  • panic-quiet: causes failed unwraps to panic with an empty message.
    This feature is enabled by default — if you'd like the unwrap error message to also show in the panic message, disable default features in your Cargo.toml as follows:
    slog-unwrap = { version = "0.9", default-features = false }
  • scope: adds support for slog-scope, which removes the need to pass a slog::Logger to the various methods.


See slog-unwraps, another crate with a similar featureset.