RS.CLIPPY.STRING_ADD

Using `x + ..` where x is a `String` instead of `push_str()`

This checker is a Clippy lint created by The Rust Project Contributors. The documentation shown here is a copy of the original documentation for: string_add. Copyright ©2025 The Rust Team. All rights reserved.

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");