pub trait Source<R: BufRead> {
// Required method
fn next_token(&mut self) -> Option<String>;
// Provided method
fn next_token_unwrap(&mut self) -> String { ... }
}
pub trait Source<R: BufRead> {
// Required method
fn next_token(&mut self) -> Option<String>;
// Provided method
fn next_token_unwrap(&mut self) -> String { ... }
}