Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::multiple_inherent_impl: multiple implementations of this structure

What it meansChecks for multiple inherent implementations of a struct The config option controls the scope in which multiple inherent impl blocks for the same struct are linted, allowing values of module (only within the same module), file (within the same file), or crate (anywhere in the crate, default). It is in the restriction group and off by default.

What you see

warning: multiple implementations of this structure
 --> main.rs:7:1
  |
7 | / impl X {
8 | |     fn other() {}
9 | | }
  | |_^
  |
note: first implementation here
 --> main.rs:4:1
  |
4 | / impl X {
5 | |     fn one() {}
6 | | }
  | |_^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#multiple_inherent_impl
  = note: requested on the command line with `-W clippy::multiple-inherent-impl`

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?

Splitting the implementation of a type makes the code harder to navigate.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

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

Flagged

struct X;
impl X {
    fn one() {}
}
impl X {
    fn other() {}
}

Write this instead

struct X;
impl X {
    fn one() {}
    fn other() {}
}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
multiple_inherent_impl = "warn"

In code

#![warn(clippy::multiple_inherent_impl)]

One run

cargo clippy -- -W clippy::multiple-inherent-impl

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

inherent-impl-lint-scope: Sets the scope (“crate”, “file”, or “module”) in which duplicate inherent impl blocks for the same type are linted.

Restrictiongroup

allowdefault level

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for multiple inherent implementations of a struct

The config option controls the scope in which multiple inherent impl blocks for the same struct are linted, allowing values of module (only within the same module), file (within the same file), or crate (anywhere in the crate, default).

Why restrict this?

Splitting the implementation of a type makes the code harder to navigate.

Example

struct X;
impl X {
    fn one() {}
}
impl X {
    fn other() {}
}

Could be written:

struct X;
impl X {
    fn one() {}
    fn other() {}
}

Configuration

inherent-impl-lint-scope: Sets the scope (“crate”, “file”, or “module”) in which duplicate inherent impl blocks for the same type are linted.

(default: "crate")

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

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