Regular Expressions

Внешняя ссылка: https://docs.rs/regex/latest/regex/

Справка по символам

1 символ

.             any character except new line (includes new line with s flag)
[0-9]         any ASCII digit
\d            digit (\p{Nd})
\D            not digit
\pX           Unicode character class identified by a one-letter name
\p{Greek}     Unicode character class (general category or script)
\PX           Negated Unicode character class identified by a one-letter name
\P{Greek}     negated Unicode character class (general category or script)

Классы символов

[xyz]         A character class matching either x, y or z (union).
[^xyz]        A character class matching any character except x, y and z.
[a-z]         A character class matching any character in range a-z.
[[:alpha:]]   ASCII character class ([A-Za-z])
[[:^alpha:]]  Negated ASCII character class ([^A-Za-z])
[x[^xyz]]     Nested/grouping character class (matching any character except y and z)
[a-y&&xyz]    Intersection (matching x or y)
[0-9&&[^4]]   Subtraction using intersection and negation (matching 0-9 except 4)
[0-9--4]      Direct subtraction (matching 0-9 except 4)
[a-g~~b-h]    Symmetric difference (matching `a` and `h` only)
[\[\]]        Escaping in character classes (matching [ or ])
[a&&b]        An empty character class matching nothing

Повторы символов

x*        zero or more of x (greedy)
x+        one or more of x (greedy)
x?        zero or one of x (greedy)
x*?       zero or more of x (ungreedy/lazy)
x+?       one or more of x (ungreedy/lazy)
x??       zero or one of x (ungreedy/lazy)
x{n,m}    at least n x and at most m x (greedy)
x{n,}     at least n x (greedy)
x{n}      exactly n x
x{n,m}?   at least n x and at most m x (ungreedy/lazy)
x{n,}?    at least n x (ungreedy/lazy)
x{n}?     exactly n x

Примеры

Замена всех совпадений в строке

Задача заменить строки, разделённые - или _ на CamelCase. При этом если строка начинается с заглавной буквы, то первое слово новой строки тоже с неё начинается:

"the-stealth-warrior" => "theStealthWarrior"
"The_Stealth_Warrior" => "TheStealthWarrior"
"The_Stealth-Warrior" => "TheStealthWarrior"

Решение:

use regex::Regex;
fn to_camel_case(text: &str) -> String {
    let before = text;
    let re = Regex::new(r"(-|_)(?P<neme>[A-z])").unwrap();
    let after = re.replace_all(before,|captures: &regex::Captures| {
        captures[2].to_uppercase()
    });
    return after.to_string();
}

Вставить пробел в camelCase

Задача разбить переход от нижнего регистра к верхнему в camelCase пробелом:

use regex::Regex;
fn solution(s: &str) -> String {
    let re = Regex::new(r"[A-Z]").unwrap(); // находим заглавную букву
    re.replace_all(s, " $0").to_string() // добавляем перед ней пробел
    // $0 означает весь найденный текст
} // camelCasingTest -> camel Casing Test

// альтернативный вариант:
fn solution(s: &str) -> String {
    Regex::new(r"([a-z])([A-Z])").unwrap()
        .replace_all(s, "$1 $2").to_string()
} // '$1 и $2' - найденные группы символов