get last index of string rust

To get the last index of a string in Rust, you can use the rfind method. Here's an example:

fn main() {
    let my_string = String::from("Hello, world!");
    let last_index = my_string.rfind("o");
    println!("Last index: {:?}", last_index);
}

In this example, the rfind method is called on the my_string variable, passing the substring "o" as an argument. The method returns an Option<usize>, which represents the index of the last occurrence of the substring in the string. If the substring is found, the index is returned as Some(index), otherwise, None is returned.

Please note that the rfind method returns the byte index, not the character index. If you're working with Unicode characters, you may need to handle them differently.