pub trait Arg {
// Required method
fn append_arg(&self, command: &mut Command);
// Provided method
fn append_option(&self, name: &str, command: &mut Command) { ... }
}pub trait Arg {
// Required method
fn append_arg(&self, command: &mut Command);
// Provided method
fn append_option(&self, name: &str, command: &mut Command) { ... }
}