Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::err_expect: called `.err().expect()` on a `Result` value
What it meansChecks for .err().expect() calls on the Result type. It is in the style group and warns by default.
What you see
warning: called `.err().expect()` on a `Result` value --> main.rs:4:3 | 4 | x.err().expect("Testing err().expect()"); | ^^^^^^^^^^^^ help: try: `expect_err` | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#err_expect = note: `#[warn(clippy::err_expect)]` on by default
Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.
Does it matter?
.expect_err() can be called directly to avoid the extra type conversion from err().
Code that works but is not idiomatic Rust. Warns by default.
How to fix it
Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.
Flagged
let x: Result<u32, &str> = Ok(10);
x.err().expect("Testing err().expect()");
Write this instead
let x: Result<u32, &str> = Ok(10);
x.expect_err("Testing expect_err");
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::err_expect)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
err_expect = "allow"One run
cargo clippy -- -A clippy::err-expectThe [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.
Settings in clippy.toml
msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml
Clippy's own documentation
What it does
Checks for .err().expect() calls on the Result type.
Why is this bad?
.expect_err() can be called directly to avoid the extra type conversion from err().
Example
let x: Result<u32, &str> = Ok(10);
x.err().expect("Testing err().expect()");
Use instead:
let x: Result<u32, &str> = Ok(10);
x.expect_err("Testing expect_err");
Configuration
-
msrv: The minimum rust version that the project supports. Defaults to therust-versionfield inCargo.toml(default:
current version)
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- needless_returnunneeded `return` statement
- new_without_defaultChecks for public types with a pub fn new() -> Self method and no implementation of Default
- len_zeroChecks for getting the length of something via .len() just to compare to zero, and suggests using .is_empty() where applicable
- double_must_usethis function has a `#[must_use]` attribute with no message, but returns a type already considered as `#[must_use]`
- duplicate_underscore_argument`a` already exists, having another argument having almost the same name makes code comprehension and documentation more difficult
- enum_variant_namesvariant name ends with the enum's name
- excessive_precisionfloat has excessive precision
- field_reassign_with_defaultChecks for immediate reassignment of fields initialized with Default::default()
- filter_map_bool_thenChecks for usage of bool::then in Iterator::filter_map
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
Up next
Related lintclippy::needless_returnunneeded `return` statementRead it next →Did this answer your question?