Clippy lints / Complexity
Clippy lint · Complexity · checked with Clippy 0.1.99
clippy::unnecessary_map_on_constructor: Suggests removing the use of a map() (or map_err()) method when an Option or Result is being constructed
What it meansSuggests removing the use of a map() (or map_err()) method when an Option or Result is being constructed. It is in the complexity group and warns by default.
Does it matter?
It introduces unnecessary complexity. Instead, the function can be called before constructing the Option or Result from its return value.
Code that does something simple in a complicated way. 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
Some(4).map(i32::swap_bytes)
Write this instead
Some(i32::swap_bytes(4))
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_on_constructor)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
unnecessary_map_on_constructor = "allow"One run
cargo clippy -- -A clippy::unnecessary-map-on-constructorThe [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
Suggests removing the use of a map() (or map_err()) method when an Option or Result
is being constructed.
Why is this bad?
It introduces unnecessary complexity. Instead, the function can be called before
constructing the Option or Result from its return value.
Example
Some(4).map(i32::swap_bytes)
Use instead:
Some(i32::swap_bytes(4))
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- too_many_argumentsChecks for functions with too many parameters
- clone_on_copyusing `clone` on type `u64` which implements the `Copy` trait
- type_complexityChecks for types used in structs, parameters and let declarations above a certain complexity threshold
- unnecessary_first_then_checkunnecessary use of `first().is_none()` to check if slice is empty
- unnecessary_get_then_checkChecks the usage of .get().is_some() or .get().is_none() on std map types
- unnecessary_literal_unwrapused `unwrap()` on `Some` value
- unnecessary_min_or_max`0` is never greater than `7_u32` and has therefore no effect
- unnecessary_operationChecks for expression statements that can be reduced to a sub-expression
- unnecessary_sort_byChecks for usage of Vec::sort_by passing in a closure which compares the two arguments, either directly or indirectly
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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Related lintclippy::too_many_argumentsChecks for functions with too many parametersRead it next →Did this answer your question?