Clippy lints / Pedantic
Clippy lint · Pedantic · checked with Clippy 0.1.99
clippy::string_add_assign: you assigned the result of adding something to this string. Consider using `String::push_str()` instead
What it meansChecks for string appends of the form x = x + y (without let!). It is in the pedantic group and off by default.
What you see
warning: you assigned the result of adding something to this string. Consider using `String::push_str()` instead --> main.rs:4:1 | 4 | x = x + ", World"; | ^^^^^^^^^^^^^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#string_add_assign = note: `-W clippy::string-add-assign` implied by `-W clippy::pedantic`
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?
It’s not really bad, but some people think that the .push_str(_) method is more readable.
Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.
How to fix it
Clippy does not fix this one automatically. Change the code by hand:
Flagged
let mut x = "Hello".to_owned();
x = x + ", World";
// More readable
x += ", World";
x.push_str(", World");
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]
string_add_assign = "warn"In code
#![warn(clippy::string_add_assign)]One run
cargo clippy -- -W clippy::string-add-assignThe [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.
Clippy's own documentation
What it does
Checks for string appends of the form x = x + y (without
let!).
Why is this bad?
It’s not really bad, but some people think that the
.push_str(_) method is more readable.
Example
let mut x = "Hello".to_owned();
x = x + ", World";
// More readable
x += ", World";
x.push_str(", World");
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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