pub trait CharString {
// Required methods
fn indexof(&self, searchstring: &str, start_index: usize) -> Option<usize>;
fn substr(&self, start_index: isize, length: isize) -> String;
fn substru(&self, start_index: usize, length: usize) -> String;
fn substr_end(&self, start_index: isize) -> String;
fn substring(&self, start_index: isize, end_index: isize) -> String;
fn str_remove(&self, start_index: usize, length: usize) -> String;
}