Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::unnecessary_result_map_or_else: Checks for usage of .map_or_else() “map closure” for Result type

What it meansChecks for usage of .map_or_else() “map closure” for Result type. It is in the suspicious group and warns by default.

Does it matter?

This can be written more concisely by using unwrap_or_else().

Code that is most likely wrong or useless. 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, ()> = Ok(0);
let y = x.map_or_else(|err| handle_error(err), |n| n);

Write this instead

let x: Result<u32, ()> = Ok(0);
let y = x.unwrap_or_else(|err| handle_error(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::unnecessary_result_map_or_else)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
unnecessary_result_map_or_else = "allow"

One run

cargo clippy -- -A clippy::unnecessary-result-map-or-else

The [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.

Suspiciousgroup

warndefault level

yesfixed by cargo clippy --fix

1.78.0added in Rust

Clippy's own documentation

What it does

Checks for usage of .map_or_else() “map closure” for Result type.

Why is this bad?

This can be written more concisely by using unwrap_or_else().

Example

let x: Result<u32, ()> = Ok(0);
let y = x.map_or_else(|err| handle_error(err), |n| n);

Use instead:

let x: Result<u32, ()> = Ok(0);
let y = x.unwrap_or_else(|err| handle_error(err));

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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