Clippy lints / Complexity
Clippy lint · Complexity · checked with Clippy 0.1.99
clippy::needless_option_as_deref: derefed type is same as origin
What it meansChecks for no-op uses of Option::{as_deref, as_deref_mut}, for example, Option<&T>::as_deref() returns the same type. It is in the complexity group and warns by default.
What you see
warning: derefed type is same as origin --> main.rs:4:9 | 4 | let b = a.as_deref(); // goes from Option<&i32> to Option<&i32> | ^^^^^^^^^^^^ help: try: `a` | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#needless_option_as_deref = note: `#[warn(clippy::needless_option_as_deref)]` 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?
Redundant code and improving readability.
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
let a = Some(&1);
let b = a.as_deref(); // goes from Option<&i32> to Option<&i32>
Write this instead
let a = Some(&1);
let b = a;
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::needless_option_as_deref)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
needless_option_as_deref = "allow"One run
cargo clippy -- -A clippy::needless-option-as-derefThe [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
Checks for no-op uses of Option::{as_deref, as_deref_mut},
for example, Option<&T>::as_deref() returns the same type.
Why is this bad?
Redundant code and improving readability.
Example
let a = Some(&1);
let b = a.as_deref(); // goes from Option<&i32> to Option<&i32>
Use instead:
let a = Some(&1);
let b = a;
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
- needless_ifsChecks for empty if branches with no else branch
- needless_lifetimesthe following explicit lifetimes could be elided: 'a
- needless_matchChecks for unnecessary match or match-like if let returns for Option and Result when function signatures are the same
- needless_option_takecalled `Option::take()` on a temporary value
- needless_question_markSuggests replacing Ok(x?) or Some(x?) with x in return positions where the ? operator is not needed to convert the type of x
- needless_splitnunnecessary use of `splitn`
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?