How do I replace specific characters idiomatically in Rust?

So I have the string "Hello World!" and want to replace the "!" with "?" so that the new string is "Hello World?"

In Ruby we can do this easily with the gsub method:

"Hello World!".gsub("!", "?")

How to do this idiomatically in Rust?

You can replace all occurrences of one string within another with str::replace:

let result = str::replace("Hello World!", "!", "?");
// Equivalently:
result = "Hello World!".replace("!", "?");
println!("{}", result); // => "Hello World?"

For more complex cases, you can use regex::Regex::replace_all from regex:

use regex::Regex;
let re = Regex::new(r"[A-Za-z]").unwrap();
let result = re.replace_all("Hello World!", "x");
println!("{}", result); // => "xxxxx xxxxx!"

Also you can use iterators and match expression:

let s:String = "Hello, world!".chars()
    .map(|x| match x { 
        '!' => '?', 
        'A'..='Z' => 'X', 
        'a'..='z' => 'x',
        _ => x
    }).collect();
println!("{}", s);// Xxxxx, xxxxx?