Clippy lint · Style · checked with Clippy 0.1.99

clippy::wrong_self_convention: Checks for methods with certain name prefixes or suffixes, and which do not adhere to standard conventions regarding how self is taken. The actual rules are: PrefixPostfixself takenself type as_none&self or &mut selfany from_nonenoneany into_noneselfany is_none&mut self or &self or noneany to__mut&mut selfany to_not _mutselfCopy to_not _mut&selfnot Copy Note: Clippy doesn’t trigger methods with to_ prefix in: Traits definition. Clippy can not tell if a type that implements a trait is Copy or not. Traits implementation, when &self is taken. The method signature is controlled by the trait and often &self is required for all types that implement the trait (see e.g

What it meansChecks for methods with certain name prefixes or suffixes, and which do not adhere to standard conventions regarding how self is taken. The actual rules are: PrefixPostfixself takenself type as_none&self or &mut selfany from_nonenoneany into_noneselfany is_none&mut self or &self or noneany to__mut&mut selfany to_not _mutselfCopy to_not _mut&selfnot Copy Note: Clippy doesn’t trigger methods with to_ prefix in: Traits definition. Clippy can not tell if a type that implements a trait is Copy or not. Traits implementation, when &self is taken. The method signature is controlled by the trait and often &self is required for all types that implement the trait (see e.g. the std::string::ToString trait). Clippy allows Pin<&Self> and Pin<&mut Self> if &self and &mut self is required. Please find more info here: https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv It is in the style group and warns by default.

Does it matter?

Consistency breeds readability. If you follow the conventions, your users won’t be surprised that they, e.g., need to supply a mutable reference to a as_.. function.

Code that works but is not idiomatic Rust. Warns by default.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

impl X {
    fn as_str(self) -> &'static str {
        // ..
    }
}

Write this instead

impl X {
    fn as_str(&self) -> &'static str {
        // ..
    }
}

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::wrong_self_convention)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
wrong_self_convention = "allow"

One run

cargo clippy -- -A clippy::wrong-self-convention

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.

Settings in clippy.toml

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

Stylegroup

warndefault level

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for methods with certain name prefixes or suffixes, and which do not adhere to standard conventions regarding how self is taken. The actual rules are:

Prefix	Postfix	`self` taken	`self` type
`as_`	none	`&self` or `&mut self`	any
`from_`	none	none	any
`into_`	none	`self`	any
`is_`	none	`&mut self` or `&self` or none	any
`to_`	`_mut`	`&mut self`	any
`to_`	not `_mut`	`self`	`Copy`
`to_`	not `_mut`	`&self`	not `Copy`

Note: Clippy doesn’t trigger methods with to_ prefix in:

Traits definition. Clippy can not tell if a type that implements a trait is Copy or not.
Traits implementation, when &self is taken. The method signature is controlled by the trait and often &self is required for all types that implement the trait (see e.g. the std::string::ToString trait).

Clippy allows Pin<&Self> and Pin<&mut Self> if &self and &mut self is required.

Please find more info here: https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv

Why is this bad?

Consistency breeds readability. If you follow the conventions, your users won’t be surprised that they, e.g., need to supply a mutable reference to a as_.. function.

Example

impl X {
    fn as_str(self) -> &'static str {
        // ..
    }
}

Use instead:

impl X {
    fn as_str(&self) -> &'static str {
        // ..
    }
}

Configuration

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

(default: true)

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

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