Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::needless_arbitrary_self_type: the type of the `self` parameter does not need to be arbitrary

What it meansThe lint checks for self in fn parameters that specify the Self-type explicitly It is in the complexity group and warns by default.

What you see

warning: the type of the `self` parameter does not need to be arbitrary
  --> main.rs:11:18
   |
11 |     pub fn bytes(self: Self) -> usize {
   |                  ^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#needless_arbitrary_self_type
   = note: `#[warn(clippy::needless_arbitrary_self_type)]` on by default
help: remove the type
   |
11 -     pub fn bytes(self: Self) -> usize {
11 +     pub fn bytes(self) -> usize {
   |

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?

Increases the amount and decreases the readability of code

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

enum ValType {
    I32,
    I64,
    F32,
    F64,
}

impl ValType {
    pub fn bytes(self: Self) -> usize {
        match self {
            Self::I32 | Self::F32 => 4,
            Self::I64 | Self::F64 => 8,
        }
    }
}

Write this instead

enum ValType {
    I32,
    I64,
    F32,
    F64,
}

impl ValType {
    pub fn bytes(self) -> usize {
        match self {
            Self::I32 | Self::F32 => 4,
            Self::I64 | Self::F64 => 8,
        }
    }
}

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_arbitrary_self_type)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
needless_arbitrary_self_type = "allow"

One run

cargo clippy -- -A clippy::needless-arbitrary-self-type

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.

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.47.0added in Rust

Clippy's own documentation

What it does

The lint checks for self in fn parameters that specify the Self-type explicitly

Why is this bad?

Increases the amount and decreases the readability of code

Example

enum ValType {
    I32,
    I64,
    F32,
    F64,
}

impl ValType {
    pub fn bytes(self: Self) -> usize {
        match self {
            Self::I32 | Self::F32 => 4,
            Self::I64 | Self::F64 => 8,
        }
    }
}

Could be rewritten as

enum ValType {
    I32,
    I64,
    F32,
    F64,
}

impl ValType {
    pub fn bytes(self) -> usize {
        match self {
            Self::I32 | Self::F32 => 4,
            Self::I64 | Self::F64 => 8,
        }
    }
}

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

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