Capitalize (and Title Case) Words In Rust

Introduction

There's no built-in method to capitalize strings in Rust. The .to_uppercase() and .to_lowercase() methods are available¹, but nothing to make only the first letter uppercase.

Most of the time, I'm looking to change a string to Title Case. That is, don't just capitalize the first word but adjust all the words accordingly. I'm using the titlecase² crate for the functionality:

---
[dependencies]
titlecase = "3.5.0"
---

use titlecase::Titlecase;

fn main() {
  let source = "alfa bravo of charlie";
  let updated = source.titlecase();
  println!("{}", updated);
}

Output:

Alfa Bravo of Charlie

Notice that the of didn't get uppercased. That's because there are some rules built into the crate that prevent "small words" from being capitalized³.

Capitalize Everything

If you really do need to capitalize everything the capitalize⁴ crate is available as well.

It only capitalizes the first word in a string. If you need to do everything you have to do something like splitting on whitespace then running the .capitalize() method on each word independently.

I'll write that up if I ever run into a case where I need it instead of titlecase.

-- end of line --

Footnotes

1 ⤴

String rust struct - docs.rs

2 ⤴

titlecase rust crate - docs.rs

Details the rules for when letters are made upper and lower case.

3 ⤴

Daring Fireball Title Case Style Guide - daringfireball.net

The original style guide the titlecase create is based off of from Daring Fireball.

4 ⤴

capitalize rust create - docs.rs