Clippy lints / Pedantic
Clippy lint · Pedantic · checked with Clippy 0.1.99
clippy::inefficient_to_string: Checks for usage of .to_string() on an &&T where T implements ToString directly (like &&str or &&String)
What it meansChecks for usage of .to_string() on an &&T where T implements ToString directly (like &&str or &&String). It is in the pedantic group and off by default.
Does it matter?
In versions of the compiler before Rust 1.82.0, this bypasses the specialized implementation of ToString and instead goes through the more expensive string formatting facilities.
Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.
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
// Generic implementation for `T: Display` is used (slow)
["foo", "bar"].iter().map(|s| s.to_string());
// OK, the specialized impl is used
["foo", "bar"].iter().map(|&s| s.to_string());
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]
inefficient_to_string = "warn"In code
#![warn(clippy::inefficient_to_string)]One run
cargo clippy -- -W clippy::inefficient-to-stringThe [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
msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml
Clippy's own documentation
What it does
Checks for usage of .to_string() on an &&T where
T implements ToString directly (like &&str or &&String).
Why is this bad?
In versions of the compiler before Rust 1.82.0, this bypasses the specialized
implementation of ToString and instead goes through the more expensive string
formatting facilities.
Example
// Generic implementation for `T: Display` is used (slow)
["foo", "bar"].iter().map(|s| s.to_string());
// OK, the specialized impl is used
["foo", "bar"].iter().map(|&s| s.to_string());
Configuration
-
msrv: The minimum rust version that the project supports. Defaults to therust-versionfield inCargo.toml(default:
current version)
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
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All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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