Cookbooks
Rust
Chapter 2. Strings
Concatenating strings

Rust:
Concatenating strings

How to:

Rust gives you a few ways to piece texts together. Let’s dig in.

Using + Operator 

let hello = "Hello".to_string();
let world = " world!";
let result = hello + world;
println!("{}", result); // Output: Hello world!

The + sticks " world!" onto "Hello", but watch out, hello needs to be a String, not a slice.

The format! Macro 

let mood = "happy";
let message = format!("Have a {} day!", mood);
println!("{}", message); // Output: Have a happy day!

format! is like println!, mixing variables into text. Super handy for templates.

Pushing to a String 

let mut tip = "Remember to".to_string();
tip.push_str(" breathe.");
println!("{}", tip); // Output: Remember to breathe.

push_str appends a slice to a String. Good for adding bits one at a time.

Deep Dive

String concatenation isn’t a new concept. It’s been around since the dawn of programming; after all, we’ve always needed to mash words together.

In Rust, a String is a growable, mutable, owned UTF-8 encoded string type. There are alternatives like &str, a string slice, which is a view into a String.

Each method has its trade-offs:

  • + operator is quick for a join or two but devours the left-hand operand (it takes ownership). Every + also allocates memory, which can add up.

  • format! doesn’t snatch any owned values, which is polite, but it can be slower due to its flexibility and allocating for each call. It’s your Swiss Army knife for string assembly.

  • push_str is efficient for a repeated add-on. It doesn’t allocate unless the String needs more space.

Rust’s focus on ownership and borrowing means that it handles strings a bit differently than languages like Python or JavaScript. This difference ensures memory safety but can also come with a learning curve.

See Also

For a deeper dive:

Capitalizing a stringConverting a string to lower case