Clippy lint · Style · checked with Clippy 0.1.99

clippy::inherent_to_string: implementation of inherent method `to_string(&self) -> String` for type `main::A`

What it meansChecks for the definition of inherent methods with a signature of to_string(&self) -> String. It is in the style group and warns by default.

What you see

warning: implementation of inherent method `to_string(&self) -> String` for type `main::A`
 --> main.rs:6:5
  |
6 | /     pub fn to_string(&self) -> String {
7 | |         "I am A".to_string()
8 | |     }
  | |_____^
  |
  = help: implement trait `Display` for type `main::A` instead
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#inherent_to_string
  = note: `#[warn(clippy::inherent_to_string)]` 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?

This method is also implicitly defined if a type implements the Display trait. As the functionality of Display is much more versatile, it should be preferred.

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

pub struct A;

impl A {
    pub fn to_string(&self) -> String {
        "I am A".to_string()
    }
}

Write this instead

use std::fmt;

pub struct A;

impl fmt::Display for A {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "I am 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::inherent_to_string)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
inherent_to_string = "allow"

One run

cargo clippy -- -A clippy::inherent-to-string

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.

Stylegroup

warndefault level

nofixed by cargo clippy --fix

1.38.0added in Rust

Clippy's own documentation

What it does

Checks for the definition of inherent methods with a signature of to_string(&self) -> String.

Why is this bad?

This method is also implicitly defined if a type implements the Display trait. As the functionality of Display is much more versatile, it should be preferred.

Example

pub struct A;

impl A {
    pub fn to_string(&self) -> String {
        "I am A".to_string()
    }
}

Use instead:

use std::fmt;

pub struct A;

impl fmt::Display for A {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "I am A")
    }
}

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

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