Clippy lint · Correctness · checked with Clippy 0.1.99

clippy::inherent_to_string_shadow_display: type `main::A` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display`

What it meansChecks for the definition of inherent methods with a signature of to_string(&self) -> String and if the type implementing this method also implements the Display trait. It is in the correctness group and denied by default (the build fails).

What you see

error: type `main::A` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display`
  --> main.rs:8:5
   |
 8 | /     pub fn to_string(&self) -> String {
 9 | |         "I am A".to_string()
10 | |     }
   | |_____^
   |
   = help: remove the inherent method from type `main::A`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#inherent_to_string_shadow_display
   = note: `#[deny(clippy::inherent_to_string_shadow_display)]` 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. The less versatile inherent method will then shadow the implementation introduced by Display.

Code that is almost certainly wrong. Denied by default: the build fails until you fix it or allow it.

How to fix it

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

Flagged

use std::fmt;

pub struct A;

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

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

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

Whole crate (Cargo.toml)

[lints.clippy]
inherent_to_string_shadow_display = "allow"

One run

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

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.

Correctnessgroup

denydefault 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 and if the type implementing this method also implements the Display trait.

Why is this bad?

This method is also implicitly defined if a type implements the Display trait. The less versatile inherent method will then shadow the implementation introduced by Display.

Example

use std::fmt;

pub struct A;

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

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

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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