Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::unnecessary_map_or: this `map_or` can be simplified
What it meansConverts some constructs mapping an Enum value for equality comparison. It is in the style group and warns by default.
What you see
warning: this `map_or` can be simplified --> main.rs:5:9 | 5 | x.map_or(false, |n| n == 5), | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unnecessary_map_or = note: `#[warn(clippy::unnecessary_map_or)]` on by default help: use a standard comparison instead | 5 - x.map_or(false, |n| n == 5), 5 + x == Some(5), |
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?
Calls such as opt.map_or(false, |val| val == 5) are needlessly long and cumbersome, and can be reduced to, for example, opt == Some(5) assuming opt implements PartialEq. Also, calls such as opt.map_or(true, |val| val == 5) can be reduced to opt.is_none_or(|val| val == 5). This lint offers readability and conciseness improvements.
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
pub fn a(x: Option<i32>) -> (bool, bool) {
(
x.map_or(false, |n| n == 5),
x.map_or(true, |n| n > 5),
)
}
Write this instead
pub fn a(x: Option<i32>) -> (bool, bool) {
(
x == Some(5),
x.is_none_or(|n| n > 5),
)
}
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_map_or)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
unnecessary_map_or = "allow"One run
cargo clippy -- -A clippy::unnecessary-map-orThe [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.
Clippy's own documentation
What it does
Converts some constructs mapping an Enum value for equality comparison.
Why is this bad?
Calls such as opt.map_or(false, |val| val == 5) are needlessly long and cumbersome,
and can be reduced to, for example, opt == Some(5) assuming opt implements PartialEq.
Also, calls such as opt.map_or(true, |val| val == 5) can be reduced to
opt.is_none_or(|val| val == 5).
This lint offers readability and conciseness improvements.
Example
pub fn a(x: Option<i32>) -> (bool, bool) {
(
x.map_or(false, |n| n == 5),
x.map_or(true, |n| n > 5),
)
}
Use instead:
pub fn a(x: Option<i32>) -> (bool, bool) {
(
x == Some(5),
x.is_none_or(|n| n > 5),
)
}
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
- unnecessary_fallible_conversionsuse of a fallible conversion when an infallible one could be used
- unnecessary_foldthis `.fold` can be written more succinctly using another method
- unnecessary_lazy_evaluationsunnecessary closure used to substitute value for `Option::None`
- unnecessary_mut_passedDetects passing a mutable reference to a function that only requires an immutable reference
- unnecessary_owned_empty_stringsusage of `&String::new()` for a function expecting a `&str` argument
- unneeded_struct_patternstruct pattern is not needed for a unit variant
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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