gistfile1.txt

fn foo(a: Option<int>, b: Option<int>, c: Option<int>) {
  arg_fail!( in "foo"
    if matches!(a: None)                      : "a missing";
    if matches!(b: Some(_))                   : "Don't need b";
    if matches!(b: None) && matches!(c: None) : "Need neither b nor c";
  )

...
}

// multimatch pattern
fn foo(a: Option<int>, b: Option<int>, c: Option<int>) {
  match (a, b, c) {
    (None, _, _)    => "a missing",
    (_, Some(_), _) => "Don't need b";
    (_, None, None) => "Need neither b nor c";
  }

...
}