Clippy lints / Restriction
Clippy lint · Restriction · checked with Clippy 0.1.99
clippy::string_add: you added something to a string. Consider using `String::push_str()` instead
What it meansChecks for all instances of x + _ where x is of type String, but only if string_add_assign does not match. It is in the restriction group and off by default.
What you see
warning: you added something to a string. Consider using `String::push_str()` instead --> main.rs:4:1 | 4 | x + ", World"; | ^^^^^^^^^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#string_add = note: requested on the command line with `-W clippy::string-add`
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 particular Add implementation is asymmetric (the other operand need not be String, but x does), while addition as mathematically defined is symmetric, and the String::push_str(_) function is a perfectly good replacement. Therefore, some dislike it and wish not to have it in their code. That said, other people think that string addition, having a long tradition in other languages is actually fine, which is why we decided to make this particular lint allow by default.
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
let x = "Hello".to_owned();
x + ", World";
Write this instead
let mut x = "Hello".to_owned();
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 = "warn"In code
#![warn(clippy::string_add)]One run
cargo clippy -- -W clippy::string-addThe [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 all instances of x + _ where x is of type
String, but only if string_add_assign does not
match.
Why restrict this?
This particular
Add implementation is asymmetric (the other operand need not be String,
but x does), while addition as mathematically defined is symmetric, and
the String::push_str(_) function is a perfectly good replacement.
Therefore, some dislike it and wish not to have it in their code.
That said, other people think that string addition, having a long tradition
in other languages is actually fine, which is why we decided to make this
particular lint allow by default.
Example
let x = "Hello".to_owned();
x + ", World";
Use instead:
let mut x = "Hello".to_owned();
x.push_str(", World");
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- string_add_assignyou assigned the result of adding something to this string. Consider using `String::push_str()` instead
- unwrap_usedChecks for .unwrap() or .unwrap_err() calls on Results and .unwrap() call on Options
- module_name_repetitionsDetects public item names that are prefixed or suffixed by the containing public module’s name
- expect_usedChecks for .expect() or .expect_err() calls on Results and .expect() call on Options
- std_instead_of_allocused import from `std` instead of `alloc`
- std_instead_of_coreused import from `std` instead of `core`
- str_to_string`to_string()` called on a `&str`
- string_lit_chars_anyChecks for <string_lit>.chars().any(|i| i == c)
- string_sliceindexing into a string may panic if the index is within a UTF-8 character
- suspicious_xor_used_as_pow`^` is not the exponentiation operator
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
Up next
Related lintclippy::string_add_assignyou assigned the result of adding something to this string. Consider using `String::push_str()` insteadRead it next →Did this answer your question?