Unicode Titlecase

Unicode titlecasing operations for chars and strings. The crate supports additional functionality for the TR/AZ locales.

Usage

Chars

To turn a char into its titlecase equivalent [char; 3]array:

use unicode_titlecase::to_titlecase;

assert_eq!(to_titlecase('A'), ['A', '\0', '\0']);
assert_eq!(to_titlecase('DŽ'), ['Dž', '\0', '\0']);
assert_eq!(to_titlecase('ffl'), ['F', 'f', 'l']);

Or use the iterator version that follows the same format as the std library. The crate defines a Trait that is implemented on char:

use unicode_titlecase::TitleCase;
assert_eq!('i'.to_titlecase().to_string(), "I");
assert_eq!('A'.to_titlecase().to_string(), "A");
assert_eq!('DŽ'.to_titlecase().to_string(), "Dž");
assert_eq!('ffl'.to_titlecase().to_string(), "Ffl");

Strings

A similar trait is defined on str. This will titlecase the first char of the string, leave the rest unchanged, and return a newly allocated String.

use unicode_titlecase::StrTitleCase;
assert_eq!("iii".to_titlecase(), "Iii");
assert_eq!("ABC".to_titlecase(), "ABC");
assert_eq!("DŽDŽ".to_titlecase(), "DžDŽ");
assert_eq!("fflabc".to_titlecase(), "Fflabc");

Alternatively, you could lowercase the rest of the str:

use unicode_titlecase::StrTitleCase;
assert_eq!("iIi".to_titlecase_lower_rest(), "Iii");
assert_eq!("ABC".to_titlecase_lower_rest(), "Abc");
assert_eq!("DŽDŽ".to_titlecase_lower_rest(), "Dždž");
assert_eq!("fflabc".to_titlecase_lower_rest(), "Fflabc");

Testing a char or str

To see if the char is already titlecase, is_titlecase is provided:

use unicode_titlecase::TitleCase;
assert!('A'.is_titlecase());
assert!('Dž'.is_titlecase());
assert!('İ'.is_titlecase());

assert!(!'a'.is_titlecase());
assert!(!'DŽ'.is_titlecase());
assert!(!'ffl'.is_titlecase());

To test if a str is already titlecase, two options are provided. The first, starts_titlecase returns true if the first character is titlecased--ignoring the rest of the str. The second starts_titlecase_rest_lower only returns true if the first char is titlecase and the rest of the str is lowercase.

use unicode_titlecase::StrTitleCase;
assert!("Abc".starts_titlecase());
assert!("ABC".starts_titlecase());
assert!(!"abc".starts_titlecase());

assert!("Abc".starts_titlecase_rest_lower());
assert!("İbc".starts_titlecase_rest_lower());
assert!(!"abc".starts_titlecase_rest_lower());
assert!(!"ABC".starts_titlecase_rest_lower());
assert!(!"İİ".starts_titlecase_rest_lower());

All testing functions work the same regardless of locale.

Locale

The Turkish and Azeri (TR/AZ) locales have different rules for how to titlecase certain characters. The to_titlecase functions assume the locale is neither of these locations. A tr_or_az version of each function is provided instead.

use unicode_titlecase::{to_titlecase_tr_or_az, StrTitleCase, TitleCase};
assert_eq!(to_titlecase_tr_or_az('i'), ['İ', '\0', '\0']);
assert_eq!('i'.to_titlecase_tr_or_az().to_string(), "İ");
assert_eq!("iIi".to_titlecase_tr_or_az(), "İIi");
assert_eq!("iIi".to_titlecase_tr_or_az_lower_rest(), "İıi");

Additionally, there are upper and lower case utilities for the Turkish and Azeri located in the tr_az module.

use unicode_titlecase::tr_az::{to_uppercase_tr_or_az, to_lowercase_tr_or_az, StrTrAzCasing};
assert_eq!(to_uppercase_tr_or_az('i').to_string(), "İ");
assert_eq!(to_lowercase_tr_or_az('I'), 'ı');
assert_eq!("İIAb".to_lowercase_tr_az(), "iıab");
assert_eq!("iıab".to_uppercase_tr_az(), "İIAB");

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Changelog

• 12 December 2025 - Release 2.5.0:
  • Upgraded to Unicode 17.0.0,
  • Upgraded to Rust 2024 edition,
  • Started a changelog

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.