造轮子笔记-result

fn (haystack: &str, needle: char) -> Option<usize> {
  for (offset, c) in haystack.char_indices() {
    if c == needle {
      return Some(offset);
    }
  }
  None
}

fn main() {
  let file_name = "foobar.rs";
  match find(file_name, '.') {
    None => println!("No file extension found."),
    Some(i) => println!("File extension: {}", &file_name[i+1..]),
  }
}

fn ok_or<T, E>(option: Option<T>, err: E) -> Result<T, E> {
  match option {
    Some(val) => Ok(val),
    None => Err(err),
  }
}