Macro either 

macro_rules! either {
    ($match:expr, $left_pattern:pat => $left_expression:expr, $right_pattern:pat => $right_expression:expr$(,)?) => { ... };
    ($match:expr, $a_pattern:pat => $a_expression:expr, $b_pattern:pat => $b_expression:expr, $c_pattern:pat => $c_expression:expr$(,)?) => { ... };
    ($match:expr, $a_pattern:pat => $a_expression:expr, $b_pattern:pat => $b_expression:expr, $c_pattern:pat => $c_expression:expr, $d_pattern:pat => $d_expression:expr$(,)?) => { ... };
    ($match:expr, $a_pattern:pat => $a_expression:expr, $b_pattern:pat => $b_expression:expr, $c_pattern:pat => $c_expression:expr, $d_pattern:pat => $d_expression:expr, $e_pattern:pat => $e_expression:expr$(,)?) => { ... };
    ($match:expr, $a_pattern:pat => $a_expression:expr, $b_pattern:pat => $b_expression:expr, $c_pattern:pat => $c_expression:expr, $d_pattern:pat => $d_expression:expr, $e_pattern:pat => $e_expression:expr, $f_pattern:pat => $f_expression:expr$(,)?) => { ... };
    ($match:expr, $a_pattern:pat => $a_expression:expr, $b_pattern:pat => $b_expression:expr, $c_pattern:pat => $c_expression:expr, $d_pattern:pat => $d_expression:expr, $e_pattern:pat => $e_expression:expr, $f_pattern:pat => $f_expression:expr, $g_pattern:pat => $g_expression:expr$(,)?) => { ... };
    ($match:expr, $a_pattern:pat => $a_expression:expr, $b_pattern:pat => $b_expression:expr, $c_pattern:pat => $c_expression:expr, $d_pattern:pat => $d_expression:expr, $e_pattern:pat => $e_expression:expr, $f_pattern:pat => $f_expression:expr, $g_pattern:pat => $g_expression:expr, $h_pattern:pat => $h_expression:expr$(,)?) => { ... };
}

Matches over the first expression and returns an either (Either, EitherOf3, … EitherOf8) composed of the values returned by the match arms.

The pattern syntax is exactly the same as found in a match arm.

Examples

let either2 = either!(Some("hello"),
    Some(s) => s.len(),
    None => 0.0,
);
assert!(matches!(either2, Either::<usize, f64>::Left(5)));

let either3 = either!(Some("admin"),
    Some("admin") => "hello admin",
    Some(_) => 'x',
    _ => 0,
);
assert!(matches!(either3, EitherOf3::<&str, char, i32>::A("hello admin")));